Fix resolve_local returning CWD-anchored URI for commonwl share lookups

[Dev9269]

Summary

resolve_local searched the XDG_DATA_HOME/commonwl share directories for a tool, found it, but returned Path(uri).as_uri() — a URI anchored to the current working directory instead of the found file. For relative URIs this raised ValueError: relative path can't be expressed as a file URI; for absolute URIs it pointed at the wrong (nonexistent) file. It also silently dropped #fragment references, and the raw uri (fragments included) was embedded in the share path so fragment lookups never matched.

Fix

• Return the URI of the actually-found share file, using is_file() instead of os.path.exists().
• Defrag the uri before building share paths, then append #fragment to the result like the direct-file branch does.
• Added the missing .cwl-extension branch's fragment handling.

Tests

New tests/test_resolver.py with 3 tests (share lookup, fragment preservation, implicit .cwl extension). All crash/return-wrong-value on the old code.

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.55%. Comparing base (b4c828c) to head (8257cd4).

Files with missing lines	Patch %	Lines
cwltool/resolver.py	81.81%	1 Missing and 1 partial ⚠️

❗ There is a different number of reports uploaded between BASE (b4c828c) and HEAD (8257cd4). Click for more details.

HEAD has 5 uploads less than BASE

Flag	BASE (b4c828c)	HEAD (8257cd4)
	16	11

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2325      +/-   ##
==========================================
- Coverage   85.01%   77.55%   -7.46%     
==========================================
  Files          46       46              
  Lines        8621     8627       +6     
  Branches     2020     2022       +2     
==========================================
- Hits         7329     6691     -638     
- Misses        817     1409     +592     
- Partials      475      527      +52     

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