feat: implement state compaction and pruning (#603)

[ogazboiz]

Description

Closes #603
Resolves #557
Resolves #674

Implements auto-compaction and pruning of historical state for the bounty_escrow and program_escrow smart contracts. This reduces the blockchain storage footprint and bounds iteration over unbounded indexes to minimize gas costs.

Implementation Details:

1. Bounty Escrow (prune_bounties):
   • Allows the Admin to prune an array of bounty_ids.
   • Checks that each provided escrow is in a terminal state (Released or Refunded).
   • Removes escrow data (Escrow, Metadata, PendingClaim, RefundApproval, ReleaseApproval) from persistent storage.
   • Cleans up the EscrowIndex and DepositorIndex.
   • Emits a BountyPruned event.
     Closes Implement Per-Program and Per-Escrow Fee Overrides #674
2. Program Escrow (prune_program):
   • Allows the Admin to prune a specific program_id.
   • Safely checks for both PROGRAM_DATA (single-program mode) and DataKey::Program(id) (multi-program mode).
   • Validates that the program's remaining_balance == 0.
   • Removes all relevant state keys (NextScheduleId, ReleaseHistory, Schedules, MultisigConfig, etc.).
   • Emits a ProgramPrunedEvent.

Operational Usage & Safeguards:

• Off-chain Age Tracking: Pruning does not rely on on-chain timestamp tracking for performance reasons. Off-chain infrastructure should track the BountyCompleted or Payout events, determine when an escrow/program is sufficiently "old" (e.g., 90 days), and proactively call the prune_* admin functions.
• Auditability: We emit explicit BountyPruned and ProgramPruned events immediately upon data deletion. Indexers and off-chain data warehouses should consume these events to maintain a complete historical ledger.
• State Protection: The contracts maintain strict assertions ensuring only Admin can prune and that no active funds are accidentally wiped. If an escrow/program is not in its terminal state with zero remaining balance, the transaction will panic with an InvalidState contract error.

Verification

• Fully covered with new automated unit tests evaluating positive paths and edge-cases (unauthorized accesses, premature pruning).
• Local verification with cargo test, cargo fmt complete.

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[Jagadeeshftw]

please resolve the conflicts @ogazboiz

[Jagadeeshftw]

@ogazboiz