Add test infrastructure with fixtures, helpers, and integration tests

- Add [lib] target to enable integration test imports
- Add rcgen and reqwest dev-dependencies for TLS and HTTP test helpers
- Create src/config/test_fixtures.rs with test_static_config() and test_dynamic_config()
- Create tests/ with integration tests, HTTP test helper (TestUpstream), and TLS test helper (SelfSignedCert)
- Add Clone derives to StaticConfig and related structs for test fixture construction
- All existing tests continue to pass

Cargo.toml

@@ -4,6 +4,10 @@ version = "0.1.0"
 edition = "2021"
 license = "MIT OR Apache-2.0"
 
+[lib]
+name = "reverse_proxy"
+path = "src/lib.rs"
+
 [[bin]]
 name = "reverse-proxy"
 path = "src/main.rs"
@@ -26,4 +30,8 @@ rustls-pki-types = "=1.12.0"
 clap = { version = "=4.6.1", features = ["derive"] }
 signal-hook = "=0.3.18"
 anyhow = "=1.0.102"
-thiserror = "=2.0.18"
+thiserror = "=2.0.18"
+
+[dev-dependencies]
+rcgen = "=0.13"
+reqwest = { version = "=0.12", features = ["json"] }