Add .NET 8 support and codec benchmarks

[RejectKid]

Summary

• publish first-class net8.0, net9.0, and net10.0 library assets
• run the full MSTest suite and packed-package consumer on all three runtimes
• validate all three assemblies inside the NuGet package
• add BenchmarkDotNet coverage for typed parsing, non-throwing parsing, allocated serialization, and caller-owned-buffer serialization
• benchmark 32-, 160-, and 1,024-byte Signal PDU payloads with allocation diagnostics
• prepare version 1.1.0 and update support/release documentation

Why

OpenDisNet previously required .NET 9 or newer even though its implementation is compatible with .NET 8. Adding a native .NET 8 asset broadens supported consumers, while the benchmark suite makes the library's performance characteristics measurable and repeatable.

Validation

• Release build: zero warnings and errors across .NET 8, 9, and 10
• MSTest: 307/307 passed on each runtime (921 runtime-specific executions)
• packed NuGet consumer: passed on .NET 8, 9, and 10
• package inspection: validated 1.1.0 metadata and all three DLL versions
• BenchmarkDotNet diagnostic runs: executed successfully on .NET 8, 9, and 10
• dotnet format --verify-no-changes
• generated schema verification: 233 classes and 72 PDUs
• NuGet vulnerability audit: clean
• direct dependency update audit: current