feat(script): add crypto and signature verification opcodes

[sgbett]

Summary

• Implement Phase 5 of the script interpreter ([Task 5] Crypto operations — hashing + signature verification #61): crypto operations and signature verification
• Add hash opcodes: OP_RIPEMD160, OP_SHA1, OP_SHA256, OP_HASH160, OP_HASH256
• Add OP_CODESEPARATOR with subscript tracking for sighash computation
• Add OP_CHECKSIG / OP_CHECKSIGVERIFY with full BSV validation (FORKID, strict DER, low-S, NULLFAIL)
• Add OP_CHECKMULTISIG / OP_CHECKMULTISIGVERIFY with classic Bitcoin M-of-N algorithm, NULLDUMMY enforcement
• Add Digest.sha1 to primitives
• Add subscript: parameter to Transaction#sighash for CODESEPARATOR support

Test plan

• Hash operation unit tests (direct and via ASM evaluation)
• P2PKH end-to-end: build tx, sign, verify through interpreter
• P2PK end-to-end verification
• CHECKSIGVERIFY with custom lock script
• 1-of-2 and 2-of-2 multisig verification
• Wrong-order signatures trigger NULLFAIL
• Non-empty dummy element triggers NULLDUMMY
• Encoding validation: missing FORKID, invalid pubkey
• CODESEPARATOR basic test
• Full suite: 906 examples, 0 failures
• RuboCop clean

Closes #61

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 88.09524% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/bsv/script/interpreter/operations/crypto.rb	90.00%	10 Missing ⚠️
lib/bsv/script/interpreter/interpreter.rb	70.58%	5 Missing ⚠️

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