Add type-aware cross-file resolver for C#

[Esderal]

Builds a global type registry (classes, interfaces, structs, records with
methods, fields, properties, and base types) from all .cs files, then
re-walks each method body with a type-tracking scope to resolve call
receivers through fields, properties, parameters, locals, this/base, and
inheritance chains. Respects using directives for namespace-scoped
disambiguation. Emits calls and instantiates edges for cross-file
resolutions only; same-file calls remain with the per-file extractor to
avoid duplication.

On a 112-file C# corpus this lifts cross-file edges from 0 to ~1445
(1028 calls + 417 instantiates) and produces god-node rankings that
match human intuition about subsystem hubs.

Known limitations (documented in comments):

• Chained calls (.A().B()) needs return-type tracking
• Extension methods needs using-static + this-parameter detection
• Generic type arguments collapsed to base type name
• Overloads: last declaration wins on name collisions

Open to feedback on:

• Whether instantiates is the right relation name, or if the project prefers creates / constructs

• Whether same-file filtering should be opt-out behind a flag (currently always on — rationale: the per-file extractor already captures same-file calls, so emitting them again would duplicate edges)

• Placement — I put the new code next to _resolve_cross_file_imports since it plays the same role for C#; happy to move it to a separate module if you'd prefer

• The _CS_NOISE concept from the earlier naive version is gone entirely in this patch — type resolution replaces name-based filtering. If you'd like me to add a safety net list anyway, let me know.

  First open-source PR for me, so please be blunt about anything that doesn't fit the project's style — I'd rather fix it than have it linger.