[cristipufu]

Summary

• System proxy support is back. Add feature flags for TLS selection #34 turned off reqwest's default features so apps can pick a TLS backend. That also turned off system-proxy, http2 and charset, so since 1.1.0 the plugin has ignored the macOS and Windows proxy settings. Those three are now listed explicitly next to json. Only the TLS default stays off, so default-tls / rustls-tls / native-tls work exactly as Add feature flags for TLS selection #34 intended.
• rust-version is now 1.85.0. It said 1.81.0, but reqwest 0.13.4 and rand 0.10 need 1.85.
• Tests for event delivery, run in CI with a new cargo test step (CI only ran cargo check before):
  • events go out in batches of 25
  • after a 5xx or a refused connection, events are kept for the next flush
  • after a 4xx, events are dropped
  • the event payload has the expected format
  • polling flushes on its own
  • an invalid App Key turns tracking off
• CI fails if OpenSSL comes back: if a default or rustls-tls build for Linux or Android has openssl-sys or native-tls in its dependency tree.
• Docs: README sections on delivery and proxies, and on the TLS backend features. Matching notes in llms.txt, whose MSRV line also said 1.70.

#34's goal still holds

TLS and proxy crates in the dependency tree (cargo tree -e normal --target <t>). Before → after:

Target	default / rustls-tls	native-tls
aarch64-linux-android	rustls → h2 rustls	native-tls openssl-sys → h2 native-tls openssl-sys
x86_64-unknown-linux-gnu	rustls → h2 rustls	native-tls openssl-sys → h2 native-tls openssl-sys
aarch64-apple-darwin	rustls → h2 rustls system-configuration	native-tls → h2 native-tls system-configuration
x86_64-pc-windows-msvc	rustls → h2 rustls windows-registry	native-tls → h2 native-tls windows-registry

OpenSSL still only appears with native-tls on Linux and Android. The proxy crates are only pulled in on macOS and Windows.

Test plan

• cargo test on stable: 8 passed
• Broke each retry rule on purpose (requeue 4xx instead of 5xx, drop on network errors, batches of 30): the matching tests fail
• cargo test on Rust 1.85 (with CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=fallback): builds and passes
• cargo check with --no-default-features --features rustls-tls and with --features native-tls
• OpenSSL guard run locally: passes as is, and fails when pointed at native-tls

Note for #38

src/test_server.rs is #38's test server without the error endpoint url field, plus server_on(listener, statuses). The network-failure test needs it to serve on a port the first flush found closed. When #38 rebases, keep its url field and add server_on. CHANGELOG.md ([Unreleased]) and the [dev-dependencies] section of Cargo.toml will also need small manual merges; a dry-run merge shows everything else merges cleanly.

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