fix(ruby-extractor): repair 7 Ruby FunctionExtractor extraction/classification bugs

[gadievron]

The Ruby tree-walk dispatched on only method/singleton_method/class/module nodes
and tracked no method visibility, so several real Ruby constructs were silently
dropped or mislabeled, degrading the function inventory and the call graph /
entry-point analysis built on it.

Fixes:

• Nested (module Outer; module Inner) and compact (module Outer::Inner) module
  names were flattened/dropped — now read via the name field (handles constant +
  scope_resolution) and concatenated as Outer::Inner instead of replaced, so
  qualified calls resolve.
• define_method(:sym) do..end / { } class-body metaprogramming now emits method
  units (parses as a call node).
• alias_method :a, :b (symbol + string forms) now extracted.
• alias new old keyword form (alias node) now extracted.
• Method visibility (private/protected/public) now threaded through the traversal
  and stored on each unit; the arg-form private :sym is consumed without leaking
  into the bare-marker toggle.
• Non-public controller methods (params helpers, before_action targets) classified
  before the controller branch, so they are no longer over-flagged as route_handler
  / entry points; public actions unchanged.
• Top-level Sinatra route DSL (get '/path' do..end) now emits route_handler units.

Method-body calls are never traversed (no false positives); non-matching
top-level/class-body calls fall through to a normal child descent.

Scope / compatibility: adds a visibility field to emitted units (additive).
unit_type for controller non-public methods narrows from route_handler to
private_method/protected_method (correctness fix; removes the entry-point
over-claim). _classify_function and _process_method_node gained an optional
visibility parameter (default public); no public API signature break. The
arg-form private :sym targeted privatization is out of scope and left as a
documented no-op toggle.

Tests: tests/parsers/ruby/test_function_extractor.py. The test imports the Ruby
extractor package-qualified (from parsers.ruby.function_extractor import
FunctionExtractor) so it does not shadow the python/php modules of the same basename
in the shared pytest session. 9 failed pre-fix -> 9 passed after the fix (8 bug
tests + 1 arg-form visibility-leak regression guard). Full suite: 185 passed, 63
skipped, 0 failed. ruff clean.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com