fix(extract): add origin_file to cross-file stubs in the six dedicated extractors

[TPAteeq]

Follow-up to #1462. ensure_named_node's cross-file fallback emits a sourceless
stub (source_file="") for a type referenced from another file. #1462 added an
internal origin_file field so that when there's no single project definition to
rewire onto, two files referencing the same bare type name get distinct stubs
(disambiguated by origin_file) instead of conflating into one shared bare-id node —
while keeping source_file="" so the #1402 rewire still collapses them onto a real
definition when one does exist.

That landed in only the generic extractor. The six dedicated extractors
(extract_go, extract_rust, extract_julia, extract_fortran,
extract_powershell, extract_objc) still lacked origin_file, so they kept
conflating.

Change

Add "origin_file": str_path to the sourceless stub in those six extractors (one line
each), matching the generic one. Only the ensure_named_node imported-type-stub path
is touched — the same path #1462 changed.

Result

Two files referencing the same bare type with no local definition:

extractor	before	after
Python (generic)	2 distinct stubs	2 (unchanged)
Go / Rust / … (dedicated)	1 conflated widget	2 distinct (a_use_a_go_widget, b_use_b_go_widget)

The #1402 rewire is unaffected (source_file stays empty): when a single real
definition exists, the stubs still collapse onto it.

Tests

• New test_go_imported_type_stubs_do_not_collide_across_source_files (mirrors the
  Python Bug: AST extractor produces duplicate node IDs for same-name imported symbols (collision, not fragmentation) #1462 test). Fails pre-fix (one conflated node), passes post-fix.
• tests/test_extract.py, tests/test_languages.py, tests/test_multilang.py: 420 pass.

Out of scope

The generic extractor has other sourceless-stub sites (inheritance bases) that also
lack origin_file. #1462 didn't touch those either, and a shared base class is more
plausibly the same type (collapsing is more often correct there), so they're kept aside for a different PR.

[safishamsi]

Thanks @TPAteeq — this completes the #1462 disambiguation across the six dedicated extractors (Julia/Fortran/Go/Rust/PowerShell/ObjC), which previously only the generic extractor had. Landed on v8 in d177f04 with your authorship, alongside #1516 (which strips the field from output — they had to ship together since this widens origin_file to more languages). Verified: a 2-file Go corpus now yields 2 distinct Widget stubs AND graph.json carries no origin_file; the #1402 rewire onto a real definition is unchanged. Closing as merged-by-port — ships in 0.9.1.