feat(validate): add --all flag to validate all example case files

[adityaraut09]

Closes #1529

Adds an --all flag to ./mfc.sh validate that loops through all example case files and reports which ones pass or fail, rather than requiring the user to check them one at a time manually.

Type of change

• New feature

Changes

• toolchain/mfc/cli/commands.py: made input positional optional (nargs="?"), added --all / -a flag to VALIDATE_COMMAND
• toolchain/mfc/validate.py: added _validate_one() helper and --all branch that globs examples/**/case.py, validates each, and prints a pass/fail summary

Testing

Verified syntax with python3 -c "import ast; ast.parse(...)". Full integration test requires the MFC build environment.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.39%. Comparing base (9906fa6) to head (88d7a31).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1620   +/-   ##
=======================================
  Coverage   60.39%   60.39%           
=======================================
  Files          83       83           
  Lines       19854    19854           
  Branches     2955     2955           
=======================================
  Hits        11990    11990           
  Misses       5863     5863           
  Partials     2001     2001           

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