feat: add output flag (#13)

## Description

The lambda CLI previously only wrote output to stdout using shell redirection.
This PR adds support for writing results to files using the `-o` flag.
This is implemented using a new `Destination` interface that mirrors the existing `Source` pattern.

Changes:
- Added `Destination` interface with `StdoutDestination` and `FileDestination` implementations.
- Added `-o` flag to CLI argument parser for output file specification.
- Updated `Config` to use `Destination` instead of direct output handling.
- Refactored main to use `Destination.Write()` for result output.
- Updated Makefile targets (`run`, `profile`, `explain`) to use `-o` flag instead of shell redirection.

### Decisions

The `-o` flag defaults to stdout when not specified or when set to `-`.
This maintains backward compatibility while providing explicit file output capability.

## Benefits

- Cleaner command-line interface without shell redirection.
- Symmetric design with `Source` interface for input.
- More portable across different shells and environments.
- Explicit output handling improves code clarity.

## Checklist

- [x] Code follows conventional commit format.
- [x] Branch follows naming convention (`<type>/<description>`).
- [ ] Tests pass (if applicable).
- [ ] Documentation updated (if applicable).

Reviewed-on: #13
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

Makefile

@@ -20,13 +20,13 @@ build:
 	chmod +x ${BINARY_NAME}
 
 run: build
-	./${BINARY_NAME} -f ./samples/$(TEST).txt > program.out
+	./${BINARY_NAME} -f ./samples/$(TEST).txt -o program.out
 
 profile: build
-	./${BINARY_NAME} -p profile/cpu.prof -f ./samples/$(TEST).txt > program.out
+	./${BINARY_NAME} -p profile/cpu.prof -f ./samples/$(TEST).txt -o program.out
 
 explain: build
-	./${BINARY_NAME} -x -p profile/cpu.prof -f ./samples/$(TEST).txt > program.out
+	./${BINARY_NAME} -x -p profile/cpu.prof -f ./samples/$(TEST).txt -o program.out
 
 graph:
 	go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof