Add Fortran/Fypp static analysis linter to catch copy-paste bugs

[sbryngelson]

Feature Request

Add a Python-based static analysis linter for Fortran/Fypp source code that catches patterns known to cause silent bugs. Integrate it into the pre-commit hook (`./mfc.sh precheck`) and CI (`lint-source.yml`).

Proposed Checks

Check	What it catches
Fypp list duplicates	Duplicate entries in `#:for VAR in [...]` broadcast/loop lists
Duplicate consecutive lines	Identical adjacent non-trivial lines (copy-paste errors)
Hardcoded byte size	`int(8._wp, ...)` patterns that assume 8-byte reals

These checks are motivated by real bugs found in the codebase. The linter would prevent regressions after the bugs are fixed.

[sbryngelson]

Fix: #1191