fix: resolve all clippy --all-targets warnings across 15 files

- gateway/mod.rs: move send_json before test module (items_after_test_module)
- memory/vector.rs: fix float_cmp, cast_precision_loss, approx_constant
- memory/chunker.rs: fix format_collect, format_push_string, write_with_newline
- memory/sqlite.rs: fix useless_vec
- heartbeat/engine.rs: fix format_collect, write_with_newline
- config/schema.rs: fix needless_raw_string_hashes
- tools/composio.rs: fix needless_raw_string_hashes
- integrations/registry.rs: fix uninlined_format_args, unused import
- tunnel/mod.rs: fix doc_markdown
- skills/mod.rs: allow similar_names in test module
- channels/cli.rs: fix unreadable_literal
- observability/mod.rs: fix manual_string_new
- runtime/mod.rs: fix manual_string_new
- examples/custom_memory.rs: add Default impl (new_without_default)
- examples/custom_channel.rs: fix needless_borrows_for_generic_args

src/config/schema.rs

@@ -1013,9 +1013,9 @@ default_temperature = 0.7
 
     #[test]
     fn composio_config_partial_toml() {
-        let toml_str = r#"
+        let toml_str = r"
 enabled = true
-"#;
+";
         let parsed: ComposioConfig = toml::from_str(toml_str).unwrap();
         assert!(parsed.enabled);
         assert!(parsed.api_key.is_none());