add net9 target and tests

[bitfaster]

No description provided.

[Copilot]

Pull Request Overview

Adds support for .NET 9.0 alongside updating defaults for .NET 8+ and extending CI/tests accordingly

• Introduce conditional default concurrency level (-1) on .NET 8+ in Defaults.cs
• Add net9.0 to both library and test project target frameworks and bump test LangVersion to 10.0
• Update LRU/LFU builder tests and expand GitHub Actions to build/test/publish on .NET 9 and .NET 8

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
BitFaster.Caching/Lru/Defaults.cs	Added #if NET8_0_OR_GREATER branch to set concurrency default
BitFaster.Caching/BitFaster.Caching.csproj	Appended net9.0 to <TargetFrameworks>
UnitTests/Lru/ConcurrentLruBuilderTests.cs	Changed .WithConcurrencyLevel(-1) to .WithConcurrencyLevel(0)
UnitTests/Lfu/ConcurrentLfuBuilderTests.cs	Changed .WithConcurrencyLevel(-1) to .WithConcurrencyLevel(0)
BitFaster.Caching.UnitTests.csproj	Appended net9.0 and bumped <LangVersion> to 10.0
.github/workflows/gate.yml	Added a second Windows job for .NET 6/8/9, updated test/coverage steps

Comments suppressed due to low confidence (3)

BitFaster.Caching/Lru/Defaults.cs:7

• Consider adding XML doc comments on ConcurrencyLevel to explain that -1 maps to the runtime default and how it differs when targeting < .NET 8.

#if NET8_0_OR_GREATER

.github/workflows/gate.yml:61

• [nitpick] The two Windows jobs share nearly identical steps; you could switch to a matrix strategy to reduce duplication and simplify adding future target versions.

  win2:

BitFaster.Caching/Lru/Defaults.cs:9

• There aren't explicit unit tests verifying the new -1 default on .NET 8+; consider adding a framework-specific test to ensure the correct behavior under .NET 9.

        public static int ConcurrencyLevel => -1;

[coveralls]

coverage: 99.086% (-0.02%) from 99.102%
when pulling 624cae9 on users/alexpeck/target9
into 28e4692 on main.