feat(base): Explicitly handle the CrossProcessLockKind::Dirty case in MediaStore

[Hywan]

This patch replaces the into_guard() call by a match over CrossProcessLockKind so that the Dirty case is explicitly handled.

The mid-term idea is to remove the into_guard() method because it is “dangerous” as it hides the Dirty case.

---

• Address [meta] _Dirty_ cross-process locks #4874

[stefanceriu]

Noice 👍

[codspeed-hq]

CodSpeed Performance Report

Merging #5855 will not alter performance

_{Comparing Hywan:feat-cross-process-lock-media (e32dfb4) with main (f61ba4f)}

Summary

✅ 50 untouched

[codecov]

Codecov Report

❌ Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.59%. Comparing base (e79f832) to head (e32dfb4).
⚠️ Report is 6 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-base/src/media/store/mod.rs	20.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5855      +/-   ##
==========================================
- Coverage   88.60%   88.59%   -0.02%     
==========================================
  Files         362      362              
  Lines      102303   102307       +4     
  Branches   102303   102307       +4     
==========================================
- Hits        90643    90635       -8     
- Misses       7440     7453      +13     
+ Partials     4220     4219       -1     

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