Merge 0.9.6 archive updates and relocate Coderive benchmark

[Copilot]

Merged the 0.9.6 archive contents into the repo and relocated the Coderive cross-language benchmark into the demo suite while trimming the external benchmark runner. Added a draft changelog capturing the release highlights.

• Runtime / lexer / parser refresh
  • Introduced CharClassifier + LexerSource, zero-allocation whitespace/comment skipping, and keyword aliases (continue→skip, return→exit).
  • Split loop/array/lambda handling into dedicated handlers and added the Exit AST node for early termination.
• Range / accumulation formulas
  • Added unified AccumulationFormula/AccumulationPattern and removed legacy linear/vector recurrence formulas.
• Stdlib & demo updates
  • JSON escaping and unicode formatting fixes, SciMath loop flow adjustments, demo suite refreshes, and new BigNumTest.
• Benchmarks
  • Moved the Coderive workload to src/main/cod/demo/src/main/test/loop/BMark.cod and removed Coderive from the cross-language runner/docs.
• Release notes
  • Added drafts/Changelog-0.9.6.md.

Example (new benchmark entrypoint):

env COD_BENCHMARK_MODE=true java -cp /tmp/coderive-compile cod.runner.CommandRunner \
  src/main/cod/demo/src/main/test/loop/BMark.cod --quiet