Add Slon fortunes benchmarks

[sebastienros]

Slon needs an end-to-end TechEmpower Fortunes workload that compares its pipelined PostgreSQL path with Npgsql under equivalent materialization and rendering behavior.

This adds Minimal API and low-level Kestrel Platform benchmark applications. Both drivers materialize messages as strings, append and sort the same model, and render the same RazorSlices template. The Slon path maps standard PostgreSQL connection settings into SlonDataSourceOptions, prepares one data-source-bound command at startup, reuses it concurrently with cancellation, and applies explicit pool and per-wire pipeline limits.

The accompanying Crank configurations clone Slon and pipelining as sibling sources, run only the Slon and Npgsql PostgreSQL jobs, and provide matching 512-connection /fortunes scenarios.

Validation included a full Release solution build, the existing test suite (792 passed, 4 skipped), all four app/driver combinations against PostgreSQL with identical sorted and HTML-escaped output, and Crank debug expansion for both configurations.

Run the benchmarks

The fork repository and branch overrides keep both the raw configuration and cloned Slon source pinned to this PR:

# Minimal: Slon
crank --config https://raw.githubusercontent.com/sebastienros/slon/refs/heads/sebros/slon-benchmarks/Slon.Benchmarks/Slon.Fortunes.Minimal/minimal-fortunes.benchmarks.yml --scenario minimal-postgresql-slon --profile aspnet-gold-lin --application.sources.Slon.repository https://github.com/sebastienros/slon.git --application.sources.Slon.branchOrCommit sebros/slon-benchmarks --json minimal-slon.json

# Minimal: Npgsql
crank --config https://raw.githubusercontent.com/sebastienros/slon/refs/heads/sebros/slon-benchmarks/Slon.Benchmarks/Slon.Fortunes.Minimal/minimal-fortunes.benchmarks.yml --scenario minimal-postgresql-npgsql --profile aspnet-gold-lin --application.sources.Slon.repository https://github.com/sebastienros/slon.git --application.sources.Slon.branchOrCommit sebros/slon-benchmarks --json minimal-npgsql.json

# Platform: Slon
crank --config https://raw.githubusercontent.com/sebastienros/slon/refs/heads/sebros/slon-benchmarks/Slon.Benchmarks/Slon.Fortunes.Platform/platform-fortunes.benchmarks.yml --scenario platform-postgresql-slon --profile aspnet-gold-lin --application.sources.Slon.repository https://github.com/sebastienros/slon.git --application.sources.Slon.branchOrCommit sebros/slon-benchmarks --json platform-slon.json

# Platform: Npgsql
crank --config https://raw.githubusercontent.com/sebastienros/slon/refs/heads/sebros/slon-benchmarks/Slon.Benchmarks/Slon.Fortunes.Platform/platform-fortunes.benchmarks.yml --scenario platform-postgresql-npgsql --profile aspnet-gold-lin --application.sources.Slon.repository https://github.com/sebastienros/slon.git --application.sources.Slon.branchOrCommit sebros/slon-benchmarks --json platform-npgsql.json