Smoke tests previously ran on one implicit torch version (whatever
pyproject.toml's unpinned bound resolved to) across all supported
python versions. Add torch_2_8/2_9/2_10/2_11 dependency groups
(build-matched torchao/torchvision per pytorch/ao issue 2919) and a
matrix.torch_group axis on the test-smoke CI job so each of the 4
torch minor versions is smoke tested independently, still covering
all 3 python versions per job via the existing nox session.

lowest_tested_torch/highest_tested_torch are renamed to torch_2_8/
torch_2_11 for a consistent naming scheme; the linux-tests/macos-tests
full-suite jobs and their Makefile targets are unchanged.

setup_env.sh now reads TORCH_GROUP directly and folds it into every
sync it runs, so make env/test/test-fast/docs/etc. all pin torch
instead of floating on whatever pyproject.toml's plain bound resolves
to. test-highest-pytorch/test-lowest-pytorch/env-highest-torch lock
their group via an inline `export TORCH_GROUP=... &&` at the top of
the recipe (rather than a hardcoded --with-torch_2_X flag), so their
name stays a promise regardless of a command-line override — verified
that GNU Make's own `override` directive achieves the same lock but
trips up the mbake Makefile formatter's duplicate-target detector,
which doesn't recognize that syntax.

--with-torch_2_X stays as a guarded alternate path for direct,
non-Make invocations of setup_env.sh; a guard now errors clearly if it
disagrees with an explicitly-set TORCH_GROUP instead of surfacing a
raw uv conflicting-groups resolver error.