Remove paket, Enforce nullness on net9.0, remove mocha

[TheAngryByrd]

Proposed Changes

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Types of changes

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• Project Infrastructure

Checklist

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• Build and tests pass locally
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

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[Copilot]

Pull Request Overview

This pull request removes Paket-related configurations and references across the solution and migrates project dependencies entirely to NuGet and PackageReference. Key changes include:

• Replacing Paket dependency management files and targets with NuGet and central package management.
• Updating build and tooling scripts to remove Paket commands and use dotnet tool commands instead.
• Minor code adjustments including a change in the disposable interface type in IcedTasks.

Reviewed Changes

Copilot reviewed 87 out of 87 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/FsToolkit.ErrorHandling.IcedTasks/CancellableTaskResultBuilderBase.fs	Updated disposable type parameters from #IDisposable to #IDisposableNull.
src/FsToolkit.ErrorHandling.AsyncSeq/paket.references	Removed Paket references in favor of PackageReference.
src/FsToolkit.ErrorHandling.AsyncSeq/FsToolkit.ErrorHandling.AsyncSeq.fsproj	Removed Paket restore targets and updated dependency management.
src/Directory.Build.props	Added conditional PackageReference configuration for Microsoft.Bcl.AsyncInterfaces and FSharp.Core.
paket.dependencies	Removed Paket dependency file.
package.json	Adjusted test commands to use node and added --noCache flags.
build/paket.references, benchmarks/paket.references	Removed Paket reference files.
build/build.fsproj	Removed Paket restore targets and switched to PackageReference for build tools.
build/build.fs	Replaced Paket.push with DotNet.nugetPush and updated test command flags.
benchmarks/benchmarks.fsproj	Updated target frameworks and introduced a PackageReference for BenchmarkDotnet.
benchmarks/SeqTests.fs	Added missing module import.
Directory.Solution.targets, Directory.Packages.props, Directory.Build.props	Updated centralized package management and build configuration.
.vscode/extensions.json, .devcontainer/devcontainer.json, .config/dotnet-tools.json	Removed Paket-related recommendations and updated tool versions.
.github/workflows/build.yml, .editorconfig	Updated Node versions and removed Paket file style rules.

Comments suppressed due to low confidence (1)

benchmarks/benchmarks.fsproj:32

• The package reference 'BenchmarkDotnet' appears to have inconsistent casing compared to the official package name 'BenchmarkDotNet'. Consider updating it to ensure consistency.

<PackageReference Include="BenchmarkDotnet"/>