feat(script): add data push and stack manipulation opcodes

[sgbett]

Summary

• Implement interpreter execution loop with two-script sequential execution, alt stack clearing between scripts, and final stack truthiness check
• Add all data push operations: OP_0, OP_1..16, OP_1NEGATE, PUSHDATA1/2/4
• Add 19 stack manipulation opcodes: DUP, 2DUP, 3DUP, DROP, 2DROP, SWAP, 2SWAP, ROT, 2ROT, OVER, 2OVER, NIP, TUCK, PICK, ROLL, DEPTH, IFDUP, TOALTSTACK, FROMALTSTACK

Closes #58

Test plan

• 56 new examples across 3 spec files (data_push, stack_ops, interpreter execution loop)
• RuboCop clean (0 offences across all 103 files)
• Full suite passes (768 examples, 0 failures)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 85.12397% with 18 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/bsv/script/interpreter/interpreter.rb	70.00%	18 Missing ⚠️

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