Fix preprocessor cache include validation

[fallintoplace]

Summary

• keep validating cached includes after the first match when ignore_time_macros is enabled
• add a regression test where the first header is unchanged and a same-size second header changes

Why

The old control flow returned immediately after hashing the first include in the ignore_time_macros path. If a later include changed, the preprocessor cache could still accept the stale result.

Testing

• cargo fmt --check
• cargo test -q compiler::preprocessor_cache::test::test_preprocessor_cache_result_checks_all_includes_when_ignoring_time_macros --lib
• cargo test -q compiler::preprocessor_cache --lib
• cargo test -q --lib

[sylvestre]

@fallintoplace in the future, don't bother adding "Testing" in comment #0, it doesn't add value for us
thanks

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.60%. Comparing base (bdbab18) to head (268196e).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2740      +/-   ##
==========================================
+ Coverage   74.56%   74.60%   +0.03%     
==========================================
  Files          70       70              
  Lines       39795    39840      +45     
==========================================
+ Hits        29675    29724      +49     
+ Misses      10120    10116       -4     

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