test(lerobot): use realistic valid shas in cache-namespacing test

[rakesh0x]

What was wrong

test_import_namespaces_source_cache_by_resolved_revision proves the cache is namespaced by the resolved Hugging Face sha. It stubbed _hf_repo_info to return the values sha-a and sha-b — neither of which would survive the production validator at src/hflow/importers/lerobot.py:239-240 (r"[0-9a-f]{7,64}"). The test passed only because the stub bypassed the validator, so a future bug in the validator or in the cache-path construction that consumes the resolved sha could not manifest in this test.

A test that uses values its own code path would reject cannot fail for the right reason.

What changed

• tests/test_lerobot_converter.py: replaced the non-hex sha-a / sha-b literals with two 40-character hexadecimal shas and bound them to local variables sha_a and sha_b. The fixture dict and both assertions now reference the variables, so the test no longer contradicts the production validator.
• No production code changes. _hf_repo_info's validator, the cache-path construction, and the rest of the test file are untouched.
• The test's contract is unchanged: two revisions that resolve to the same sha share one cache directory, a different sha gets its own. branch-a and tag-a still resolve to the same sha on purpose — that is the two-revisions-one-cache leg of the contract.

The two shas were chosen so a reader can tell them apart at a glance (one starts with a1b2, the other with f0e1), not just at the last character.

How the fix was validated

• uv run ruff check --fix — passed
• uv run ruff format — passed (no formatting changes)
• uv run ty check — passed
• uv run pytest -q tests/test_lerobot_converter.py — 35 passed
• uv run pytest -q — 1421 passed, 12 skipped (the two pre-existing test_checks.py failures around camera_motion and Lucas-Kanade optical flow are unrelated to this change — they reproduce on plain origin/main without this branch's commit and concern a different module; out of scope for this PR).

Proof the relevant test passes

$ uv run pytest -q tests/test_lerobot_converter.py::test_import_namespaces_source_cache_by_resolved_revision
.                                                                        [100%]
1 passed in 0.12s

Out of scope

The two test_checks.py failures observed on the full suite are pre-existing and unrelated to this change. They will be addressed in a separate PR.

closes #371

[kstonekuan]

LGTM, merging.

Both shas satisfy the validator that made this worth changing, and the old ones did not:

sha_a      len=40  [0-9a-f]{7,64} accepts: True
sha_b      len=40  [0-9a-f]{7,64} accepts: True
'sha-a'    len= 5                 accepts: False

a1b2c3... against f0e1d2... is the right call on DoD 3: distinguishable at a glance, so the two-revisions-one-cache leg still reads as two revisions and one cache rather than two forty-character blurs. Naming them as constants and commenting why branch-a and tag-a share one is what keeps that legible.

On the out-of-scope note: those two test_checks.py failures do not reproduce here. On your branch merged with current main, tests/test_checks.py is 35 passed and the full suite is 1436 passed / 6 skipped with nothing failing. The likely cause is a sync without the optional extras, which is the same trap that has caught two other contributors this week:

uv sync --locked --all-extras
uv run pytest -q

--all-extras is the documented form in CONTRIBUTING, and without it a handful of vision-dependent tests behave differently. Worth confirming before opening that separate PR, since there may be nothing to fix.

Closes #371.