fix(fortran): emit calls edges for function invocations

[Synvoya]

Summary

Fortran function calls (y = f(x)) emit no calls edge. Only call sub(...) (subroutine) calls were captured.

Root cause

walk_calls handled subroutine_call but not call_expression, which is how tree-sitter-fortran represents a function invocation:

assignment_statement
  identifier "x"
  call_expression        <-- unhandled
    identifier "compute"

So every function-to-function call was dropped.

Fix

Handle call_expression. Fortran uses the same name(...) syntax for array indexing (arr(i)), so — unlike subroutine_call — the callee is resolved against procedures defined in the file (target_nid in seen_ids) before emitting. Array accesses whose name isn't a defined procedure produce no edge, so they can't fabricate spurious calls.

Verification

• f = g() -> calls(f, g); call sub() still works; arr(3) array access -> no edge.
• Added a function + caller to the fixture and a regression test.
• pytest tests/test_languages.py -> 300 passed, 13 skipped (13 fortran).
• ruff check -> clean.

[safishamsi]

Merged into v8 as b8f41c7 (your authorship). The array-indexing guard is the right call and it holds — adversarial smoke confirmed z = dbl(a) emits a call while z = arr(3) (same name(...) syntax) does not. Full suite 2774. Ships next release.