[Repo Assist] Prepare release 8.5.0 (#499)

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Assist](https://github.com/fsprojects/FSharp.TypeProviders.SDK/actions/runs/24058266578).*

## Summary

Bumps the version to **8.5.0** by adding an entry to `RELEASE_NOTES.md`
covering all changes merged since 8.4.0:

- **Performance**: O(1) assembly-name dictionary lookup in `convTypeRef`
(#493)
- **Performance**: Avoid O(n²) allocations in `ILMethodDefs` name-index
construction; reuse lazy caches in `TargetTypeDefinition` for
`GetField`/`GetPropertyImpl`/`GetEvent` (#497)
- **Refactor**: `save`-based caching for
`GetField`/`GetEvent`/`GetNestedType` on `ProvidedTypeDefinition`;
`Dictionary` in `ILNestedExportedTypesAndForwarders` (#498)
- **CI**: NuGet and FAKE build caching (#495)

No code changes — RELEASE_NOTES.md only.

## Test Status

✅ 126/126 tests pass (`dotnet test
tests/FSharp.TypeProviders.SDK.Tests.fsproj -c Release`).




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Author: github-actions[bot]

RELEASE_NOTES.md

@@ -1,3 +1,10 @@
+#### 8.5.0 - April 7, 2026
+
+- Performance: O(1) assembly-name dictionary lookup in `convTypeRef` #493
+- Performance: Avoid O(n²) allocations in `ILMethodDefs` name index construction; use lazy caches in `TargetTypeDefinition` for `GetField`/`GetPropertyImpl`/`GetEvent` #497
+- Refactor: Add `save`-based caching to `GetField`/`GetEvent`/`GetNestedType` on `ProvidedTypeDefinition`; use `Dictionary` in `ILNestedExportedTypesAndForwarders` #498
+- CI: Add NuGet and FAKE build caching to CI workflows #495
+
 #### 8.4.0 - March 31, 2026
 
 - Bug fix: Fix `GetEnumUnderlyingType()` to correctly handle non-Int32 enum underlying types #470