Release v0.3.9: New Built-in Functions for TC18 Support

This release adds 8 new built-in functions to support TriCore TC18 instruction
behavior descriptions, along with comprehensive testing and documentation.

Major Changes:
- Added 8 new built-in functions: ssov, suov, carry, borrow, reverse16,
  leading_ones, leading_zeros, leading_signs
- Full support in RTL interpreter, simulator generator, and VS Code extension
- Comprehensive test coverage (20 Python tests + 18 VS Code extension tests)
- Complete documentation updates

New Built-in Functions:

Saturation Functions:
- ssov(value, width) - Signed Saturation on Overflow
  * Saturates to 0x7FFFFFFF (max) or 0x80000000 (min) for 32-bit
  * Needed for: ADDS, ADDS.H, ABSDIFS, ABSDIFS.H, ABSS, ABSS.H, RSUBS, MULS
- suov(value, width) - Unsigned Saturation on Overflow
  * Saturates to 0xFFFFFFFF (max) or 0x00000000 (min) for 32-bit
  * Needed for: ADDS.U, ADDS.HU, RSUBS.U

Carry/Borrow Functions:
- carry(operand1, operand2, carry_in) - Calculate Carry Out
  * Returns 1 if carry occurs, 0 otherwise
  * Needed for: ADDC, ADDX, SUBC, SUBX
- borrow(operand1, operand2, borrow_in) - Calculate Borrow Out
  * Returns 1 if borrow occurs, 0 otherwise
  * Needed for: SUBC, SUBX

Bit Manipulation Functions:
- reverse16(value) - Reverse 16-bit value (bit order reversal)
  * Needed for: Bit-reverse addressing mode instructions
- leading_ones(value) - Count Leading Ones
  * Needed for: CLO, CLO.H instructions
- leading_zeros(value) - Count Leading Zeros
  * Needed for: CLZ, CLZ.H instructions
- leading_signs(value) - Count Leading Sign Bits
  * Needed for: CLS, CLS.H instructions

Implementation:

Python Package:
- isa_dsl/runtime/rtl_interpreter.py: Added 8 new function implementations
- isa_dsl/generators/simulator.py: Updated to generate calls to helper methods
- isa_dsl/generators/templates/simulator.j2: Added 8 new helper methods
- isa_dsl/model/validator.py: Updated to recognize new built-ins

VS Code Extension:
- isa-validator.ts: Added validation for all new functions with argument count checks
- isa-completion-provider.ts: Added autocomplete suggestions with documentation
- builtin-functions.test.ts: Added 18 new test cases

Documentation:
- docs/DSL_Specification.md: Added comprehensive documentation for all new functions
- docs/LANGUAGE_SERVER.md: Updated built-in function validation documentation
- docs/TESTING.md: Updated test documentation

Testing:
- tests/rtl_builtins/test_new_builtins.py: New test file with 20 test cases
  * 8 direct RTL interpreter tests
  * 12 simulator integration tests
- tests/rtl_builtins/test_data/builtins.isa: Added 12 new test instructions
- All edge cases covered (overflow, underflow, boundary values)

Test Results:
- Python: 213 tests passing (20 new tests added)
- VS Code Extension: 74 tests passing (18 new tests added)
- Total: 287 tests, all passing, 0 skipped, 0 failed

Version Updates:
- pyproject.toml: 0.3.8 → 0.3.9
- vscode_extension/isa/package.json: 0.3.8 → 0.3.9
- vscode_extension/isa/packages/extension/package.json: 0.3.8 → 0.3.9
- vscode_extension/isa/packages/language/package.json: 0.3.8 → 0.3.9

Files Changed:
- New: tests/rtl_builtins/test_new_builtins.py (20 test cases)
- Modified: isa_dsl/runtime/rtl_interpreter.py (8 new functions)
- Modified: isa_dsl/generators/simulator.py (function mapping)
- Modified: isa_dsl/generators/templates/simulator.j2 (8 helper methods)
- Modified: isa_dsl/model/validator.py (built-in list)
- Modified: vscode_extension/isa/packages/language/src/isa-validator.ts (validation)
- Modified: vscode_extension/isa/packages/language/src/isa-completion-provider.ts (completions)
- Modified: vscode_extension/isa/packages/language/test/builtin-functions.test.ts (18 tests)
- Modified: tests/rtl_builtins/test_data/builtins.isa (12 test instructions)
- Modified: docs/DSL_Specification.md (new functions documentation)
- Modified: docs/LANGUAGE_SERVER.md (validation documentation)
- Modified: docs/TESTING.md (test documentation)
- Modified: RELEASE_NOTES.md (v0.3.9 entry)
- Modified: All version files (0.3.8 → 0.3.9)

Breaking Changes: None
Migration: No changes required, all new functions are additive
