add bitwise not, unsigned right shift, and exponentiation operators

[cs01]

Summary

• Implement ~ (bitwise NOT) unary operator — ~0 now correctly returns -1
• Implement >>> (unsigned/logical right shift) binary operator — 255 >>> 4 returns 15
• Implement ** (exponentiation) binary operator — 2 ** 3 returns 8, uses llvm.pow.f64
• Add ** to both TS and native parsers
• Unskip bitwise/basic-bitwise.ts test (all bitwise ops now work)
• Add arithmetic/exponentiation.ts test fixture

Test plan

• npm run verify:quick passes
• Both JS and native compilers pass all new tests
• Self-hosting Stage 1 passes