feat: add ContainerGuard for RAII container lifecycle management

Implements #216. ContainerGuard provides automatic container lifecycle
management for tests using the RAII pattern:

- Builder pattern for configuration (remove_on_drop, stop_on_drop,
  keep_on_panic, capture_logs, reuse_if_running)
- Automatic cleanup on drop (stop and/or remove containers)
- Dynamic port mapping via host_port()
- Log capture on test failures with keep_on_panic
- Container reuse support for faster test iterations
- Works with any Template implementation

New testing feature flag enables the module. Requires template-redis
as a dependency for the Template trait.

Author: joshrotenberg

Cargo.toml

@@ -50,6 +50,9 @@ template-nginx = ["reqwest"]
 template-redis-sentinel = ["template-redis"]
 template-redis-stack = ["template-redis"]
 
+# Testing utilities (requires at least one template feature)
+testing = ["template-redis"]
+
 [dependencies]
 tokio = { version = "1.46", features = [
     "process",

src/lib.rs

@@ -402,6 +402,7 @@ pub mod error;
 pub mod platform;
 pub mod prerequisites;
 pub mod stream;
+
 #[cfg(any(
     feature = "templates",
     feature = "template-redis",
@@ -464,6 +465,8 @@ pub mod stream;
     feature = "template-nginx"
 ))]
 pub mod template;
+#[cfg(feature = "testing")]
+pub mod testing;
 
 pub use stream::{OutputLine, StreamHandler, StreamResult, StreamableCommand};