…adata with enums; generic parsers updated; tests adjusted; add InterfaceLayout scaffolding

* Refactor moduledata parsing using field offset tables (Issue #55)

This commit refactors moduledata parsing for Go versions 1.16-1.24 to use
a data-driven approach with field offset tables instead of repetitive
version-specific switch statements.

Changes:
- Add objfile/layouts.go with generic field offset layout system
- Add objfile/layouts_test.go with comprehensive test coverage
- Refactor objfile/objfile.go to use generic parser for Go 1.16-1.24
- Reduce code from ~430 lines of switches to ~60 lines of generic code

Benefits:
- 85% code reduction for supported versions (430 → 62 lines)
- Adding new Go versions requires only ~8 lines of layout data
- Single parsing logic eliminates duplicate code
- Comprehensive test suite ensures correctness

Testing:
- All existing tests pass
- New tests verify layout offsets match struct definitions
- Backward compatibility tests ensure identical output
- Tested against real Go 1.17.2 binary (testproject)

Fixes #55

* Extend moduledata refactoring to Go 1.5-1.15 (Issue #55)

Extends the layout table approach to older Go versions (1.5-1.15),
eliminating 228 lines of repetitive switch statements.

Changes:
- Add layout definitions for Go 1.5-1.6, 1.7, and 1.8-1.15 to layouts.go
- Add validateAndConvertModuleData_Legacy() for Go 1.7-1.15
- Add validateAndConvertModuleData_Legacy_NoTypes() for Go 1.5-1.6
- Refactor objfile.go case "1.2" block (228 lines → 75 lines)
- Add comprehensive tests for legacy versions (17 new test cases)

Benefits:
- 67% code reduction in legacy version handling
- Consistent parsing approach across Go 1.5-1.24 (20 versions)
- Improved maintainability and extensibility
- Single source of truth for moduledata layouts

Testing:
- All existing unit tests pass
- Added TestLayoutOffsets_Legacy_Versions (6 subtests)
- Added TestVersionMapping_Legacy (11 subtests)
- Total: 17 new test cases validating legacy version support

Code Metrics:
- objfile/objfile.go: 1,783 → 1,628 lines (-155 lines)
- objfile/layouts.go: 436 → 564 lines (+128 lines infrastructure)
- objfile/layouts_test.go: 380 → 590 lines (+210 lines tests)
- Net: -155 lines of duplicate code eliminated

Addresses maintainer feedback on PR #78 (moduledata portion).
Type parsing refactoring (Phase 2) to follow in next commit.

* Extend type parsing refactoring to all Go versions (Issue #55)

Refactors type parsing (ParseType_impl) to use the layout table approach,
eliminating 158 lines of repetitive version-specific switch statements.

Changes:
- Add RtypeLayout system to layouts.go for Go 1.5-1.24
- Add parseRtypeGeneric() for generic type parsing
- Add getRtypeFieldOffset() helper function
- Refactor ParseType_impl() to use generic parser (208 lines → 50 lines)
- Add comprehensive tests for Rtype layouts (23 test cases)

Benefits:
- 76% code reduction in type parsing (208 lines → 50 lines)
- Consistent parsing approach for all Go 1.5-1.24 type structures
- Single source of truth for Rtype layouts
- Improved maintainability

Testing:
- All existing tests pass
- Added TestRtypeLayoutOffsets (3 subtests)
- Added TestRtypeVersionMapping (20 subtests)
- Total: 23 new test cases validating Rtype support

Code Metrics:
- objfile/objfile.go: 1,628 → 1,470 lines (-158 lines)
- objfile/layouts.go: 564 → 786 lines (+222 lines infrastructure)
- objfile/layouts_test.go: 590 → 748 lines (+158 lines tests)

Combined with Phase 1:
- Total code reduction: 313 lines from objfile.go
- ModuleData + Type parsing: ~650 lines → ~125 lines (81% reduction)

Completes maintainer feedback on PR #78 (type parsing portion).

* PR #78: Change #1 complete – replace string field metadata with enums; generic parsers updated; tests adjusted; add InterfaceLayout scaffolding