feat(tiles): add hot metadata cache for warm zoom >= 9 hits

[stef-k]

Summary

• add an in-process tile metadata hot cache for zoom >= 9 warm hits using IMemoryCache
• add the TileMetadataHotCacheSizeMB admin setting, migration, and live MB-to-entry hint in Admin Settings
• invalidate hot metadata entries on purge/eviction/delete paths and preserve throttled LastAccessed updates
• add focused tests covering warm-hit seeding/bypass, revalidation refresh, fetch population, purge/eviction invalidation, and admin validation

Test Plan

• dotnet build
• dotnet test tests\\Wayfarer.Tests\\Wayfarer.Tests.csproj --filter "FullyQualifiedName~Wayfarer.Tests.Services.TileCacheServiceTests"
• dotnet test tests\\Wayfarer.Tests\\Wayfarer.Tests.csproj --no-build --filter "FullyQualifiedName~Wayfarer.Tests.Controllers.AdminSettingsControllerTests|FullyQualifiedName~Wayfarer.Tests.Controllers.TilesControllerTests"

Closes #217

[stef-k]

Addressed the review findings around hot-hit LastAccessed throttling.

Changes in c5a21e4:

• replaced the non-atomic touch-marker TryGetValue + Set flow with an atomic per-tile claim in TileMetadataHotCache
• only start the 5-minute cooldown after a successful DB persist
• abort and release the claim on missing-row / failure paths so later requests can retry immediately
• added regression tests covering atomic claim behavior and abort-to-retry recovery

Re-verified with:

• dotnet build
• dotnet test tests\\Wayfarer.Tests\\Wayfarer.Tests.csproj --no-build --filter "FullyQualifiedName~Wayfarer.Tests.Services.TileCacheServiceTests|FullyQualifiedName~Wayfarer.Tests.Controllers.AdminSettingsControllerTests|FullyQualifiedName~Wayfarer.Tests.Controllers.TilesControllerTests"

[stef-k]

Reviewed current PR head 4d5c1e7 after the hot-hit throttling fix.

Assessment:

• no findings on the current implementation
• warm zoom >= 9 hits now avoid the DB metadata read while expired/miss paths continue through the existing revalidation/fetch pipeline
• request-level tile limiting and outbound upstream limiting remain unchanged, so existing OSM-facing protections are still respected
• admin setting validation/UI are aligned with the intended -1 or 16..512 MB behavior

Also added the 1.2.28 changelog entry to prepare the release.