base: Add media retention policy to EventCacheStore

[zecakeh]

Allows to prevent the media cache from growing indefinitely by setting different limitations like size or last access time. I tried to select sensible defaults for those values.

Currently cleanups must be triggered manually, a future PR will add the possibility to run a regular cleanup task so they happen automatically.

[stefanceriu]

Sounds awesome but it's a biggie so I think it's safer to pass it over to somebody more familiar with the SDK, congrats Benji! 😁

[codecov]

Codecov Report

Attention: Patch coverage is 95.87629% with 20 lines in your changes missing coverage. Please review.

Project coverage is 84.33%. Comparing base (7f4e79e) to head (02a3630).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/matrix-sdk-sqlite/src/event_cache_store.rs	90.32%	6 Missing ⚠️
...rix-sdk-base/src/event_cache_store/memory_store.rs	91.37%	5 Missing ⚠️
...s/matrix-sdk-base/src/event_cache_store/wrapper.rs	75.00%	5 Missing ⚠️
...rates/matrix-sdk-base/src/event_cache_store/mod.rs	88.57%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3918      +/-   ##
==========================================
+ Coverage   84.18%   84.33%   +0.15%     
==========================================
  Files         267      268       +1     
  Lines       28036    28554     +518     
==========================================
+ Hits        23601    24082     +481     
- Misses       4435     4472      +37     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[zecakeh]

Rebased on main to solve a conflict.

[bnjbvr]

Hi, thanks for the PR, since this is a large commit it might take a bit of time to get to review it. I'll try my best.