Release v0.3.7: Format Constant Fields Feature

This release introduces format constant fields, allowing constant values to be
defined directly in instruction format field definitions. This eliminates
repetition when multiple instructions share the same constant field value.

Major Changes:
- Added format constant fields syntax: `field_name: [lsb:msb] = constant_value`
- Constants are automatically encoded in all instructions using the format
- Constants cannot be overridden in instruction encodings (validation enforced)
- Constants do not appear as operands in disassembly output

Features:
- Grammar support in both textX and Langium
- Comprehensive validation (Python and TypeScript)
- Full code generation support (assembler, simulator, disassembler)
- VS Code extension validation and syntax highlighting
- Backward compatible with existing ISA specifications

Implementation:
- Extended grammar rules in isa.tx and isa.langium
- Added constant_value field to FormatField model class
- Updated all code generation templates
- Added validation in Python validator and TypeScript validator
- Created comprehensive test suite (12 new tests)
- Added example file demonstrating usage

Documentation:
- Updated DSL_Specification.md with "Constant Fields in Formats" section
- Updated test counts in all documentation (193 Python tests, 55 VS Code tests)
- Updated RELEASE_NOTES.md with detailed feature documentation

Test Results:
- 193 Python tests passing (12 new tests for format constants)
- 55 VS Code extension tests passing
- All tests passing, 0 skipped, 0 failed

Version Updates:
- pyproject.toml: 0.3.6 → 0.3.7
- vscode_extension/isa/package.json: 0.3.6 → 0.3.7
- vscode_extension/isa/packages/extension/package.json: 0.3.6 → 0.3.7
- vscode_extension/isa/packages/language/package.json: 0.3.6 → 0.3.7

Files Changed:
- Core: grammar, model, validator, code generation templates
- VS Code: grammar, validator
- Tests: new test_format_constants.py (12 tests)
- Examples: new format_constants_example.isa
- Documentation: DSL_Specification.md, RELEASE_NOTES.md, test counts

