Implement RIPEMD-160 precompile (0x03)

Summary

Implement the RIPEMD-160 precompile at address 0x03.

Prerequisites

• #34 — Add precompile routing in CALL path

Specification

• Address: 0x03
• Input: arbitrary bytes
• Output: 32 bytes — 20-byte RIPEMD-160 hash, left-padded with 12 zero bytes
• Gas: 600 base + 120 per word (32-byte chunks, rounded up)

Implementation Guide

1. Create lib/eevm/precompiles/ripemd160.ex:
   • Gas: 600 + 120 * ceil(byte_size(input) / 32)
   • Hash: :crypto.hash(:ripemd160, input) → 20 bytes → left-pad to 32 bytes
2. Register in Precompiles.execute/3 for address 0x03.
3. Tests — empty input, known test vectors, output is 32 bytes (12 zero prefix + 20 hash), gas calculation.

Acceptance Criteria

• [ ] Returns correct RIPEMD-160 hash, left-padded to 32 bytes
• [ ] Gas calculated correctly
• [ ] Tests pass

Reference

• Yellow Paper §E.2