Add GitVersion-based release packaging for NuGet artifacts

[Copilot]

The repository was packing NuGet artifacts in CI, but versions were still manually derived and the packages stopped at workflow artifacts. This change moves package versioning to GitVersion-generated SemVer and wires tagged builds to publish the resulting packages into both GitHub Releases and the repository NuGet feed.

• Semantic versioning

  • Added a repo-local GitVersion tool manifest and GitVersion.yml.
  • Switched package version generation from ad hoc CI suffixing to GitVersion-driven PackageVersion.

• Workflow release publishing

  • Extended the existing build workflow to:
    • fetch full history for version calculation
    • restore local tools
    • compute semVer once per run
    • use that version for both BitNetSharp.Core and BitNetSharp.App packages
  • Added v* tag handling so tagged builds:
    • upload .nupkg files to the corresponding GitHub release
    • push the same packages to GitHub Packages NuGet feed

• Documentation

  • Added a GitBook page describing local version calculation and tagged release behavior.
  • Linked the new page from docs/README.md and docs/SUMMARY.md.

• Packaging flow example

  - name: Calculate semantic version
    id: gitversion
    run: |
      echo "semVer=$(dotnet tool run dotnet-gitversion /output json /showvariable SemVer /nonormalize)" >> "$GITHUB_OUTPUT"
  
  - name: Pack BitNetSharp.Core
    run: dotnet pack src/BitNetSharp.Core/BitNetSharp.Core.csproj \
      --configuration Release \
      --no-build --no-restore \
      -p:PackageVersion=${{ steps.gitversion.outputs.semVer }}

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[Copilot]

Pull request overview

This PR introduces GitVersion-driven semantic versioning for the repo’s NuGet artifacts and extends the CI workflow so v* tag builds publish packages to both GitHub Releases and GitHub Packages.

Changes:

• Add a repo-local GitVersion tool manifest and GitVersion.yml for SemVer calculation.
• Update the CI workflow to compute a single version per run, pack with that version, and publish on version tags.
• Add GitBook documentation for local version calculation and tagged release publishing, and link it from the docs index.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
dotnet-tools.json	Adds GitVersion.Tool to the repo’s .NET tool manifest.
GitVersion.yml	Defines GitVersion configuration (branch/tag handling and increments).
.github/workflows/build.yml	Fetches full history, computes SemVer, uses it for packing, and publishes on tags.
docs/releases-and-packaging.md	Documents local GitVersion usage and tag-based publishing behavior.
docs/README.md	Adds link to the new releases/packaging page.
docs/SUMMARY.md	Adds the new page to GitBook navigation.