BIP375: Add test vectors + runner

[macgyver13]

This PR adds the test runner reference.py and test_vectors.json for demonstrating BIP 375 behavior.
Care was taken to minimize dependencies required to evaluate the test vectors.

Dependencies (copied from related BIPs):

• bip352_utils.py - partial copy from bip-0352/bitcoin_utils.py
• dleq_374.py - copied from bip-0374/reference.py
• secp256k1_374.py - copied from bip-0374/secp256k1.py

Test generation files:

• tests/ - test vector generation scripts

Feedback welcome @andrewtoth @achow101 @josibake

Test runner output

Invalid test cases: 13
=== Running Invalid Test Cases ===
Test 1: Missing DLEQ proof for ECDH share
Test 2: Invalid DLEQ proof
Test 3: Non-SIGHASH_ALL signature with silent payments
Test 4: Mixed segwit versions with silent payments
Test 5: Silent payment outputs but no ECDH shares
Test 6: Global ECDH share without DLEQ proof
Test 7: Wrong SP_V0_INFO field size
Test 8: Mixed eligible and ineligible input types
Test 9: Wrong ECDH share size
Test 10: Wrong DLEQ proof size
Test 11: Label without SP_V0_INFO
Test 12: Address mismatch
Test 13: Both global and per-input ECDH shares

Valid test cases: 4
=== Running Valid Test Cases ===
Test 14: Single signer with global ECDH share
Test 15: Multi-party with per-input ECDH shares
Test 16: Silent payment with change detection
Test 17: Multiple silent payment outputs to same scan key

Note: Additional Proof of Concept examples can be found in bip375-examples repo.