feat: add comprehensive tracing instrumentation

[joshrotenberg]

Adds tracing integration throughout the library for observability.

Changes

• Instrument CommandExecutor::execute_command() with command name, runtime, timeout, exit status, and stdout/stderr output
• Instrument Template lifecycle methods (start, stop, remove, is_running, wait_for_ready) with container state tracking
• Instrument retry logic in DebugExecutor with attempt counts, delays, and backoff calculations
• Add tracing documentation to lib.rs with usage examples showing how to enable and configure tracing
• Update version numbers in feature flag examples to 0.9

Usage

Users can enable tracing by adding a subscriber:

use tracing_subscriber::EnvFilter;

tracing_subscriber::fmt()
    .with_env_filter(EnvFilter::from_default_env())
    .init();

Then control verbosity with RUST_LOG:

# Show all docker-wrapper traces
RUST_LOG=docker_wrapper=trace cargo run

# Show only command execution info
RUST_LOG=docker_wrapper::command=debug cargo run

# Show template lifecycle events
RUST_LOG=docker_wrapper::template=debug cargo run

Closes #196