Modernize to net8.0/net10.0 and ship as a native-AOT tool

[Mpdreamz]

assembly-rewriter targets net8.0/net10.0, ships as a self-contained native-AOT executable on five platforms, and parses its CLI with Nullean.Argh instead of CommandLineParser.

Prompt summary: Modernize this repo's build tooling the way curb, assembly-differ, and nupkg-validator already do — bump the stale target frameworks, move CLI parsing onto a source-generated parser, and package the tool as native-AOT dotnet tools per-RID with a framework-dependent fallback.

Why

The project still targeted netcoreapp3.0, netcoreapp3.1, net5.0, and net6.0 — all out of support. CommandLineParser parses arguments through reflection, which native AOT trims away, blocking the AOT packaging this PR adds. The pinned build tools, nupkg-validator 0.5.0 and assembly-differ 0.14.0, predate net8.0+ output: the old nupkg-validator throws loading this project's assembly for validation, and the old assembly-differ mis-resolves the dotted net8.0 framework folder when diffing.

What

CLI parsing

AssemblyRewriterCommand.cs replaces the CommandLineParser wiring in Program.cs with Nullean.Argh, registered via MapAndRootAlias<AssemblyRewriterCommands>() with [DefaultCommand] so the original bare invocation (no subcommand) still works. Options.cs drops its CommandLineParser attributes and becomes a plain data holder. Doc-comment-driven flag names and short aliases (-i/--in, -o/--out, -r/--resolvedir, -k/--keyfile, -m/--merge, -v/--verbose) only get picked up this way — a bare method-group Map/MapRoot delegate silently ignores them, filed as nullean/argh#74.

Target frameworks

assembly-rewriter.csproj moves from netcoreapp3.0;netcoreapp3.1;net5.0;net6.0 to net8.0;net10.0. global.json and build/scripts/scripts.fsproj follow suit, and <Nullable>enable</Nullable> is on for new code with a NoWarn list covering the legacy code that predates nullable annotations.

Native-AOT packaging

The project gains linux-x64, linux-arm64, win-x64, win-arm64, and osx-arm64 as RuntimeIdentifiers, plus a framework-dependent any fallback, with PublishAot, PublishSelfContained, and StripSymbols scoped to builds targeting a specific RID.

Package staging, signing, and CI

generatePackages stages a full dotnet pack and keeps only the root and any packages, replacing the unsigned obj/ copy of this project's own assembly that dotnet pack puts inside the any package with the correctly signed bin/ one. .github/workflows/ci.yml adds an aot-pack matrix job building each RID on a matching runner, ahead of a build job that downloads and merges the artifacts before packages get published.

Build tool pins

dotnet-tools.json bumps nupkg-validator from 0.5.0 to 0.10.1 and assembly-differ from 0.14.0 to 0.16.0.

Verify

./build.sh build generatepackages validatepackages generateapichanges -s true
dotnet tool install --add-source build/output assembly-rewriter
assembly-rewriter --in path/to/Some.dll --out path/to/Some.Rewritten.dll