Preview: validate against libvcs subprocess-trimming

[tony]

Summary

• Preview / not for merge. Pins libvcs to its in-development subprocess-trimming branch (Return command output verbatim by default libvcs#538) via [tool.uv.sources] to validate the downstream impact of libvcs's verbatim-default subprocess output capture.
• That libvcs change flips run() to return output verbatim by default (so git diff round-trips and applies), with a trim=True opt-in for bare-value reads; get_revision() and the scalar rev_parse/rev_list paths stay bare.

Result

vcspull's full suite passes unchanged against the libvcs branch:

$ uv run py.test
1087 passed (27 snapshots passed)

No vcspull code changes were needed — it already strips defensively where it compares scalar output, and get_revision() remains a bare SHA on the libvcs branch.

Changes

• pyproject.toml: add [tool.uv.sources] pinning libvcs to the branch.
• uv.lock: resolves libvcs to the branch build.

Before merge

Drop the [tool.uv.sources] pin and re-lock once libvcs releases the change; the version constraint (libvcs>=0.43.0,<0.44.0) is unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.85%. Comparing base (0347015) to head (969ecea).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #556   +/-   ##
=======================================
  Coverage   83.85%   83.85%           
=======================================
  Files          30       30           
  Lines        4354     4354           
  Branches      873      873           
=======================================
  Hits         3651     3651           
  Misses        467      467           
  Partials      236      236           

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