find: reject invalid -newerXY predicates like GNU

[l46983284-cpu]

Summary

find accepted invalid predicates such as -neweraBcmty because the -newerXY parser matched a valid prefix instead of the whole argument. GNU find reports those as unknown predicates.

This change:

• anchors -newerXY matching so only exact X∈{a,B,c,m} / Y∈{a,B,c,m,t} forms parse
• reports unknown predicates with GNU-style wording: unknown predicate \…'` (as in the issue sample)
• adds unit + integration coverage for the issue bug(find): Invalid predicates accepted #782 cases
• fixes a pre-existing unit test that incorrectly glued -follow -newerXY into one argv token (that only worked while the regex was unanchored)

Note: open PR #724 only rewords the unknown-predicate message for ordinary unrecognized args. This PR also fixes the real #782 root cause (prefix match on -newerXY) and uses the GNU backtick/apostrophe quote shape from the issue.

Test plan

• cargo test --lib (227 passed)
• cargo test --test test_find invalid_newerxy_predicate_is_rejected
• Integration harness covers find -neweraBcmty . failing with unknown predicate \-neweraBcmty'`

Fixes #782

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.88%. Comparing base (f38dbe5) to head (f483825).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/find/matchers/mod.rs	88.88%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #784      +/-   ##
==========================================
- Coverage   91.89%   91.88%   -0.01%     
==========================================
  Files          35       35              
  Lines        7217     7233      +16     
  Branches      376      376              
==========================================
+ Hits         6632     6646      +14     
- Misses        442      444       +2     
  Partials      143      143              

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[github-actions]

Commit dc04cfa has test result changes:

GNU findutils testsuite:

Test results comparison:
  Current:   TOTAL: 495 / PASSED: 417 / FAILED: 77 / SKIPPED: 1
  Reference: TOTAL: 495 / PASSED: 416 / FAILED: 78 / SKIPPED: 1

Changes from main branch:
  TOTAL: +0
  PASSED: +1
  FAILED: -1

Test improvements (1):
  + tests/find/refuse-noop

bfs testsuite:

Test results comparison:
  Current:   TOTAL: 315 / PASSED: 267 / FAILED: 42 / SKIPPED: 6
  Reference: TOTAL: 313 / PASSED: 267 / FAILED: 40 / SKIPPED: 6

Changes from main branch:
  TOTAL: +2
  PASSED: +0
  FAILED: +2

New test failures (2):
  - gnu/files0_from_ok
  - gnu/okdir_path_relative

[codspeed-hq]

Merging this PR will not alter performance

✅ 20 untouched benchmarks

---

_{Comparing l46983284-cpu:fix/find-unknown-newerxy-predicate (f483825) with main (f38dbe5)}

[HackingRepo]

one job fails because of intermittent issues https://github.com/uutils/findutils/actions/runs/29574082323/job/87867034162

[github-actions]

Commit f483825 has test result changes:

GNU findutils testsuite:

Test results comparison:
  Current:   TOTAL: 495 / PASSED: 417 / FAILED: 77 / SKIPPED: 1
  Reference: TOTAL: 495 / PASSED: 416 / FAILED: 78 / SKIPPED: 1

Changes from main branch:
  TOTAL: +0
  PASSED: +1
  FAILED: -1

Test improvements (1):
  + tests/find/refuse-noop

bfs testsuite:

Test results comparison:
  Current:   TOTAL: 314 / PASSED: 267 / FAILED: 41 / SKIPPED: 6
  Reference: TOTAL: 314 / PASSED: 267 / FAILED: 41 / SKIPPED: 6

New test failures (1):
  - gnu/okdir_path_empty

Test improvements (1):
  + gnu/files0_from_ok