refactor: eliminate respond_to? violations, add thorough specs

[ronaldtse]

Summary

• Eliminate all respond_to? violations — 6 occurrences replaced with proper type checks, no-op base methods, and model-driven declarations
• Add model-driven id to UmlModel — UML Model elements CAN have xmi:id in XMI schema; now properly declared
• Add thorough specs for all perf implementations (248 → 299 examples)

Code changes

File	Change
parser_pipeline.rb	Remove respond_to?(:valid_encoding?) and respond_to?(:build_index)
root.rb	Add no-op build_index (OCP: pipeline calls unconditionally)
parsing.rb	Replace respond_to?(:read) with is_a?(String)
ea_root/code_generation.rb	Abstract classes get root_tag { nil }
ea_root/extension_lifecycle.rb	Check klass.root_tag truthiness instead of respond_to?
uml/uml_model.rb	Add id attribute and mapping
sparx/index.rb	Remove respond_to?(:id) and respond_to?(:packaged_element) guards

Spec additions

• namespace_detector_spec.rb (new): regex extraction, version detection, regex vs Nokogiri parity across all fixtures
• index_spec.rb (rewritten): concrete assertions against known fixture data, EAStub indexing, parent tracking, minimal XML edge case
• parser_pipeline_spec.rb: step isolation, context mutation verification, base Root compatibility
• extension_loading_spec.rb: abstract vs stereotype root_tag tests
• versioning_spec.rb: fallback idempotency guard, detect_register, parse_with_detected_version
• fixtures.rb: remove stale ea-xmi-2.4.2.xmi entry (file doesn't exist)