Feature/contract upgrade mechanism

[devJaja]

Description

Adds a safe, planned upgrade path for all deployed CrowdPass Soroban contracts via a shared upgradeable crate.
Implements admin-controlled upgrades with a ~24h timelock, version tracking, emergency pause, and on-chain event
emissions for full transparency.

Fixes #100

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Test coverage improvement

Changes Made

• Added shared contracts/upgradeable library with timelock upgrade flow, pause/unpause, version tracking, admin
  transfer, and event emissions
• Integrated upgrade mechanism into all 6 contracts: event_manager, marketplace, ticket_factory, ticket_nft,
  tba_registry, tba_account
• Fixed pre-existing compile errors in event_manager (missing DataKey/Error variants, missing
  try_promote_from_waitlist, missing escrow balance tracking)
• Fixed pre-existing broken unit tests across ticket_nft, ticket_factory, tba_account, tba_registry (unclosed
  delimiters, spurious .unwrap() on non-Result types, broken test file structure)
• Updated integration tests to match updated constructor/initializer signatures

Testing

• All workspace unit tests pass (cargo test --workspace)
• WASM release build passes (cargo build --target wasm32-unknown-unknown --release)
• Integration tests pass (10/10)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Additional Notes

Upgrade flow:

1. Admin calls schedule_upgrade(new_wasm_hash) — emits upgrade_scheduled with effective-at ledger
2. After ~24h (17,280 ledgers), admin calls commit_upgrade() — swaps WASM, bumps version, emits upgraded
3. Admin can call cancel_upgrade() at any point before commit

Emergency pause via pause() / unpause() blocks all state-mutating operations instantly without requiring an upgrade
cycle.

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