feat(dotnet): add QueryDoctor.SqlCommenter.EFCore package

[veksen]

Summary

• Add QueryDoctor.SqlCommenter.EFCore 8.0.0 — an EF Core interceptor that appends SQLCommenter-formatted comments to SQL queries for query attribution and observability
• Includes 37 tests (unit tests with NSubstitute + SQLite in-memory integration tests)
• Published to NuGet.org as QueryDoctor.SqlCommenter.EFCore

What's included

Library (dotnet/sqlcommenter-efcore/src/):

• SqlCommenterInterceptor — intercepts all 6 EF Core command methods (Reader/NonQuery/Scalar x sync/async)
• QueryTaggingContext — AsyncLocal ambient context for explicit query tagging
• QueryTagInfo — comment formatting with URL encoding, sorted keys per SQLCommenter spec
• DbContextOptionsBuilderExtensions — ergonomic .AddSqlCommenter() registration
• SqlCommenterOptions — configuration (enabled, stack inspection, framework version)

Tests (dotnet/sqlcommenter-efcore/test/):

• 12 QueryTagInfo formatting tests
• 11 SqlCommenterInterceptor unit tests (mocked DbCommand)
• 4 SQLite in-memory integration tests (real SQL pipeline)
• 8 QueryTaggingContext lifecycle tests
• 2 extension method registration tests

CI: .github/workflows/dotnet-efcore-tests.yaml — runs on dotnet/** changes

Usage:

options.UseSqlServer(connectionString).AddSqlCommenter();

Test plan

• dotnet build — 0 errors, 0 warnings
• dotnet test — 37/37 passing
• dotnet pack — produces .nupkg + .snupkg

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