feat: minimize default features and complete EventListener coverage

[fannnzhang]

Summary

Mobile-friendly Cargo features plus OkHttp-aligned call observability, including the four P2s from the local review.

Features and dependency pins

• Workspace pins now disable unused default features (tokio/full, hyper/full, tower/timeout, rustls logging, extra futures-util macros).
• Production crates request only the Tokio (rt/net/time/io-util/sync) and Hyper (client/http1/http2) features they use.
• Compression splits into independently selectable gzip / deflate / brotli / zstd. compression remains the default umbrella. compression-core is the internal module gate; enabling it with no codec compiles and injects no Accept-Encoding.
• Built-in Jar moves behind the cookies feature (still default-on). Custom CookieJar implementations do not need it. json now also gates logger pretty-print.

EventListener lifecycle

• EventListenerFactory::create runs at Client::new_call / Call::try_clone, so cancel-before-execute and dispatcher events share a listener.
• New callbacks (all defaulted): dispatcher queue, proxy select, tls_handshake, request/response body start, request_failed, response_failed, canceled, retry_decision, follow_up_decision, cache hit/miss/conditional/satisfaction.
• Public types: ProxyEvent, TlsHandshake.

Body-event correctness (review P2s)

• Present zero-length bodies (explicit_empty, from_static(b"")) emit request_body_start / request_body_end 0 at Hyper handoff instead of being skipped.
• Try-send failures are classified from per-attempt CallContext flags, not Hyper TrySendError commitment, so upload errors do not also emit response_failed.
• response_body_start waits for first data (or close without a prior read), matching OkHttp 4.3 / the trait docs.

Compatibility

• Default feature users keep TLS, all codecs, and cookies.
• default-features = false dependents that used Jar must now enable cookies, and must declare any extra Tokio/Hyper features their own crate needs.

Test plan

• cargo check -p openwire --no-default-features --features compression-core --lib
• cargo check -p openwire --no-default-features --features gzip --lib
• cargo clippy -p openwire-core -p openwire --lib -- -D warnings
• cargo test -p openwire-core --lib request_exchange_observation
• cargo test -p openwire --lib compression::tests
• Integration coverage for empty present bodies, upload request_failed, absent-body response_failed, delayed response_body_start, plus existing body/dispatcher/pool event tests
• Full cargo test --workspace --all-features not run locally (disk ~2.5Gi free)