feat(contracts): add governance and subscription-payments contracts

[ayinde38]

• Add governance contract with proposal creation, token-weighted voting, and delegation
• Implement proposal lifecycle: Active → Queued → Executed with time-lock enforcement
• Add voting mechanisms supporting For/Against/Abstain choices with quorum validation
• Implement single-level delegation allowing vote power accumulation
• Add subscription-payments contract for recurring payment management
• Update workspace Cargo.toml to include new governance and subscription-payments members
• Add comprehensive test suites for both contracts with edge case coverage
• Enable protocol parameter governance with off-chain execution support

Closes: #156
Closes: #157

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[ONEONUORA]

Nice implementation @ayinde38