find: make `InodeMatcher` & `LinksMatcher` unix-only

[cakebaker]

This PR is a refactoring that makes the implementations of InodeMatcher and LinksMatcher unix-only. And moves the error handling for other platforms to where we handle -inum and -links.

The refactoring is done to get rid of two "field x is never read" warnings on Windows (see, for example, https://github.com/uutils/findutils/actions/runs/9271426702/job/25506758917#step:6:185)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 60.51%. Comparing base (5b19ea2) to head (cd0e119).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #393 +/- ## ========================================== + Coverage 60.48% 60.51% +0.02% ========================================== Files 32 32 Lines 4069 4067 -2 Branches 895 893 -2 ========================================== Hits 2461 2461 Misses 1254 1254 + Partials 354 352 -2 ```

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[github-actions[bot]]

GNU testsuite comparison:

Run GNU findutils tests: GNU tests summary = TOTAL: 718 / PASS: 433 / FAIL: 282 / ERROR: 2
Run GNU findutils tests: Changes from main: PASS +0 / FAIL +0 / ERROR +0 / SKIP +0 
Run BFS tests: Changes from main: PASS +0 / SKIP +0 / FAIL +0
Run BFS tests: BFS tests summary = TOTAL: 288 / PASS: 182 / SKIP: 1 / FAIL: 105

[sylvestre]

@hanbings maybe we should display it only when here are changes. it will be too noisy otherwise

[hanbings]

@hanbings maybe we should display it only when here are changes. it will be too noisy otherwise

OK, I'll open a new PR to work on it.