refactor(benchmarks): unify benchmark structure, enable CLI parameterization, run matrix, add CSV/JSON/pretty output

- All benchmarks now use a unified base mixin for setup/teardown (BenchmarkWithScope).
- Added args package support: CLI flags for choosing benchmarks, chain counts, nesting depths, output format.
- Support for running benchmarks in matrix mode (multiple parameter sets).
- Machine-readable output: csv, json, pretty-table.
- Loop and naming lint fixes, unused imports removed.

benchmark_cherrypick/pubspec.yaml

@@ -9,6 +9,7 @@ environment:
 dependencies:
   cherrypick:
     path: ../cherrypick
+  args: ^2.7.0
 
 dev_dependencies:
   lints: ^5.0.0