perf(pull): apply CANFAR permissions without subprocesses

[tjzegmott]

CANFAR downloads currently start separate recursive chgrp and chmod processes for every destination folder. Replace those subprocesses with native traversal, resolve chime-frb-rw once per transfer, and preserve existing mode bits while adding group write permission. Permission failures remain best effort, and symlinks are not followed.

The branch now includes current main; its final diff preserves the newer JSON output, transfer handling, and dependency updates.

Validation:

• 273 non-CADC tests pass on Python 3.10 and 3.14; 9 credential-dependent tests are excluded.
• 10 new permission tests cover nested files, symlinks and replacement races, missing groups, unreadable owned files, and per-file failures.
• All pre-commit hooks pass.
• A local temporary-directory benchmark measured 89.3 ms to 3.10 ms across 40 small directories. A single directory with 2,000 files measured 15.6 ms to 17.3 ms, so the benefit is reduced process-launch overhead rather than a universal speedup. CANFAR filesystem performance has not been measured.

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[Copilot]

Pull request overview

Replaces shell-based chgrp/chmod invocations in get_files() with native Python equivalents (os.walk + shutil.chown + os.chmod) on the canfar site to remove per-folder subprocess overhead.

Changes:

• Added import stat.
• Replaced two os.system(...) calls per folder with an os.walk loop that applies group ownership (chime-frb-rw) and g+w bit using native APIs.
• Preserves the prior fire-and-forget semantics by swallowing OSError per file/directory.

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[coveralls]

coverage: 64.656% (-2.0%) from 66.667% — perf-optimize-chown-chmod-17468975491131157657 into main

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.93617% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.70%. Comparing base (f52a917) to head (9108c95).
⚠️ Report is 68 commits behind head on main.

Files with missing lines	Patch %	Lines
dtcli/src/functions.py	95.23%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #157       +/-   ##
===========================================
+ Coverage   67.08%   78.70%   +11.62%     
===========================================
  Files          16       31       +15     
  Lines        1686     4128     +2442     
===========================================
+ Hits         1131     3249     +2118     
- Misses        555      879      +324     

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