default enable compression, update test helpers (#10102)

set `enable_request_compression` flag to default-enabled.

update integration test helpers to decompress `zstd` if flag set.

codex-rs/core/tests/common/Cargo.toml

@@ -25,6 +25,7 @@ tokio-tungstenite = { workspace = true }
 walkdir = { workspace = true }
 wiremock = { workspace = true }
 shlex = { workspace = true }
+zstd = { workspace = true }
 
 [dev-dependencies]
 pretty_assertions = { workspace = true }