Add timeseries collection tests

[danielfrankcom]

This change adds general tests for timeseries collections.

The aim here is to test the runtime semantics unique to timeseries collections. This includes granularity upgrade/downgrade via collMod, field immutability (timeField/metaField cannot be changed), default index creation, etc.

A separate file was added under the createIndexes command path because timeseries collections have a distinct set of index type restrictions. These are createIndexes-specific behaviors that belong alongside the other createIndexes tests rather than in the collections directory, consistent with how capped/clustered collection tests don't duplicate command-level validation that already has a better home.

The TimeseriesCollection helper in target_collection.py was refactored to accept a raw timeseries_options dict and optional create_options dict, replacing the previous individual fields. This makes it easier to test arbitrary timeseries configurations without needing to add a new field for each option. The existing collStats test that used the old interface was updated accordingly.

[documentdb-triage-tool]

🤖 Auto-triaged by documentdb-triage-tool.

Applied: compatibility test, enhancement
Project fields suggested: Component test-coverage · Priority P2 · Effort L · Status Needs Review
Confidence: 0.88 (mixed)

Reasoning

component from path globs (test-coverage, test-framework); effort from diff stats (882+19 LOC, 8 files); LLM: Adds new timeseries collection test coverage across multiple files including a helper refactor and new index restriction tests, touching several test directories.

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