test: add reader benchmark suite

[chaliy]

What

Adds a Mira reader benchmark example comparing FetchKit against Jina Reader, Firecrawl, Trafilatura/Readability, and Crawl4AI on fixed public pages.

Why

Gives the project a repeatable real-web quality benchmark for token count, link preservation, main-content precision, table/code retention, and metadata preservation.

How

• Adds the reader_bench Mira example with Rust Learn, docs.rs reqwest, Wikipedia Rust, GitHub fetchkit, and Stack Overflow Python main pages.
• Adds target adapters for FetchKit, Jina Reader, Firecrawl, and CLI-based Trafilatura/Crawl4AI.
• Documents install/run configuration for optional tool targets.

Risk

• Medium
• Benchmark depends on live public pages and third-party services, so scores, latency, and availability can drift.

Checklist

• Unit tests are passed
• Smoke tests are passed
• Documentation is updated
• Specs are up to date and not in conflict

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace
• RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps
• cargo build --workspace --exclude fetchkit-python --release
• doppler run --project everruns-dev --config dev -- bash -lc 'PATH="/Users/mykhailochalyi/.codex/worktrees/cc71/fetchkit/.bench-bin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/pkg/env/global/bin:/opt/homebrew/bin:/Users/mykhailochalyi/.codex/tmp/arg0/codex-arg0DzDLth:/Users/mykhailochalyi/.cache/codex-runtimes/codex-primary-runtime/dependencies/bin:/opt/homebrew/opt/curl/bin:/Users/mykhailochalyi/.local/bin:/opt/homebrew/opt/rustup/bin:/Users/mykhailochalyi/.cargo/bin:/opt/homebrew/sbin:/Applications/Codex.app/Contents/Resources" mira --example reader_bench run' (25/25 passed)