Reduce allocations for SdkResolverService

[Erarndt]

Fixes #

Context

Changes Made

Testing

Notes

[Copilot]

Pull Request Overview

This PR aims to reduce memory allocations in the SdkResolverService by modifying how resolvers are enumerated and cached.

• Removed an unnecessary ToList() call to avoid extra allocation.
• Refactored the locking mechanism when caching resolver instances.

Comments suppressed due to low confidence (2)

src/Build/BackEnd/Components/SdkResolution/SdkResolverService.cs:229

• Removing the ToList() call avoids unnecessary allocations, but please verify that the resolvers enumerable is not enumerated more than once, which could incur performance penalties if iterated multiple times.

sdkReferenceLocation);

src/Build/BackEnd/Components/SdkResolution/SdkResolverService.cs:277

• Acquiring the lock for every resolver manifest could increase contention; consider checking the cache outside the lock first if thread-safety can be maintained to further reduce overhead.

IReadOnlyList<SdkResolver> newResolvers;