pgrep: optimize length detection

[Franklin-Qi]

When calculating the length, the ^$ character needs to be removed if the -x parameter is present.

Closes: #635

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 18.93%. Comparing base (6ac0e01) to head (fb69db0).
⚠️ Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
src/uu/pgrep/src/process_matcher.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #636      +/-   ##
==========================================
+ Coverage   18.77%   18.93%   +0.16%     
==========================================
  Files          66       66              
  Lines        9752     9773      +21     
  Branches      516      518       +2     
==========================================
+ Hits         1831     1851      +20     
- Misses       7921     7922       +1     

Flag	Coverage Δ
macos_latest	7.00% <41.17%> (+0.08%)	⬆️
ubuntu_latest	19.30% <66.66%> (+0.16%)	⬆️
windows_latest	0.02% <0.00%> (-0.01%)	⬇️

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[Krysztal112233]

could you please add some unittest to test your modification and make sure no regression if possible?

[Franklin-Qi]

could you please add some unittest to test your modification and make sure no regression if possible?

@Krysztal112233 Thank you for your review; I have added test cases in this area.

[sylvestre]

why this change ?

[Franklin-Qi]

@sylvestre Thanks for your reply. When the --fcntl option is present, executing cargo test --all on ubuntu 25.10 will report an error:

failures:

---- test_pgrep::test_pidfile_fcntl_locked stdout ----
bin: "/home/ysq/code/procps/target/debug/procps"
run: /home/ysq/code/procps/target/debug/procps pgrep --logpidfile --pidfile /tmp/.tmpWhyLfW

thread 'test_pgrep::test_pidfile_fcntl_locked' (23065) panicked at tests/by-util/test_pgrep.rs:668:10:
Command was expected to succeed. code: 1
stdout = 
 stderr = pgrep: Pidfile /tmp/.tmpWhyLfW is not locked

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    test_pgrep::test_pidfile_fcntl_locked

test result: FAILED. 197 passed; 1 failed; 1 ignored; 0 measured; 0 filtered out; finished in 4.92s

error: test failed, to rerun pass `-p procps --test tests`

There is also a note: “CI runner doesn't support flock --fcntl”. Therefore, modifications were made to handle this error.