Add custom-constraints-from-PLEXOS templater

[nick-gorman]

What this does

ISPyPSA needs AEMO's REZ / sub-region export limits as custom constraints, but
they don't come out of the IASR workbook in a usable shape. AEMO does express
them in its PLEXOS model, as export-group constraints, so we extract them from
there. This PR adds the templater that turns that extract into ISPyPSA's three
custom-constraint tables:

• custom_constraints: one row per constraint (id + direction)
• custom_constraints_lhs: the left-hand-side terms (which unit, what coefficient)
• custom_constraints_rhs: the per-timeslice limit on the right

It sits behind the use_new_table_format flag (committed off) and only runs at
sub_regions granularity.

The bit worth understanding first

The RHS and most of the LHS are a straight translation from the PLEXOS extract.
The one judgement call is batteries, and it's worth knowing before you read
the code.

PLEXOS encodes battery participation as per-constraint LP variables (e.g.
SWQLD1 Battery - 2h) whose layout doesn't map cleanly onto any IASR unit (see
#110). Rather than mirror that, the templater builds the LHS in
two passes:

1. PLEXOS pass: translate the raw LHS rows (generators, batteries, lines,
   nodes) into ISPyPSA's term schema, dropping anything that doesn't map to a
   known unit.
2. Battery injection: for each constraint, find where its surviving
   new-entrant generator terms sit (REZ / sub-region), then add every IASR
   new-entrant battery at those same locations.

One format note: the constraints come out with region-prefixed timeslices
(qld_peak_demand) rather than the bare names (peak_demand) the rest of the
templater uses. A follow-up PR will bring the rest of the transmission
functionality onto this format so the constraints flow through end-to-end.

Where it lives

ISPyPSA/
├─ src/ispypsa/templater/
│  ├─ custom_constraints_from_plexos.py   the templater (PLEXOS extract → the 3 tables)
│  ├─ plexos/7.5/*.csv                     the extract it reads at runtime (already on main)
│  ├─ create_template.py                   wires it in at sub_regions; tracks the 3 outputs
│  └─ mappings.py, transmission.py         now share one canonical-timeslice vocabulary
├─ scripts/
│  ├─ extract_plexos_constraints.py        PLEXOS XML → the extract above (already on main)
│  └─ workbook_extract_constraint.py       independent workbook-route LHS, validation only
└─ tests/test_templater/
   ├─ test_custom_constraints_from_plexos.py   templater unit tests
   ├─ test_custom_constraints_validation.py    PLEXOS route vs workbook route reconciliation
   └─ data/custom_constraints_validation/      fixtures (plexos/ + workbook/)

Supporting changes

A few small things ride along: the templater is wired into
create_ispypsa_inputs_template (gated to sub_regions, its three outputs
tracked as task targets); the two IASR summary tables it needs are added to the
required-tables list; and the canonical timeslice vocabulary is promoted into
mappings so the templater and the existing transmission code share one copy.

Validation

Pulling these constraints out of PLEXOS takes enough translation that we didn't
want to take the output on trust. So the PR cross-checks the templater against a
second, fully independent reconstruction of each constraint built straight from
the IASR workbook (scripts/workbook_extract_constraint.py). The goal is both
to confirm the PLEXOS route produces the right LHS and to understand exactly
where and why the two sources differ. The two routes share no code:

• The PLEXOS route is the production templater reading the PLEXOS extract.
• The workbook route looks each constraint up in
  rez_group_constraint_summary, parses its Terms into (coefficient, body)
  pairs, and expands them. A REZ id (e.g. Q1) becomes every generator,
  battery and electrolyser tagged with that REZ ID across the IASR unit summary
  tables; an interconnector path id (e.g. CQ-NQ) becomes a single link_flow
  term. Coefficients can be implicit (Q1 is 1.0), signed (- CQ-NQ is -1.0)
  or explicit (0.78 * V7).

test_custom_constraints_validation.py runs both routes over five constraints
(NQ1, NET1, WV1, CQ1, MN1) and asserts the LHS term sets match
exactly, save for an explicit EXPECTED_DELTAS table. A new mismatch in either
direction fails the test, and so does an expected one going missing.

The documented differences come down to two things:

1. Geographic lookup for existing plant. Every IASR unit carries both a
   fine-grained REZ ID and a coarser sub-region, and they usually agree. The
   workbook route expands by REZ ID; PLEXOS includes existing plant by
   sub-region. The handful of boundary plants where the two tags point
   different places are the only generator diffs. For example EMERASF1 (REZ
   Q4, sub-region NQ) lands in NQ1 under PLEXOS but CQ1 under the
   workbook, so the one fact shows up on both sides of the comparison.
2. Electrolysers. PLEXOS routes electrolyser load through its Purchaser
   class, which the templater drops by design (hydrogen demand isn't modelled),
   so they appear as workbook-only load terms.

Batteries don't appear as a difference either: the templater rebuilds battery
participation from the IASR new-entrant set rather than translating PLEXOS' own
battery layout, so neither PLEXOS' constraint-scoped battery variants nor its
quiet exclusion of 4h-duration batteries surface in the comparison.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/ispypsa/iasr_table_caching/local_cache.py	74.28% <ø> (ø)
src/ispypsa/templater/create_template.py	92.50% <100.00%> (+3.31%)	⬆️
...spypsa/templater/custom_constraints_from_plexos.py	100.00% <100.00%> (ø)
src/ispypsa/templater/mappings.py	100.00% <100.00%> (ø)
src/ispypsa/templater/transmission.py	98.70% <100.00%> (-0.01%)	⬇️

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