feat: Implement StateJournal and in-memory snapshots for state rollback

[SIDDHANTCOOKIE]

Addressed Issues:

Previously, the node relied heavily on full copy.deepcopy() operations of the entire state dictionary. This PR replaces that with a highly optimized two-tier rollback architecture:

1. Transaction-level Undo Log (StateJournal)
   Problem: When validating transactions inside a block, the node was making an expensive deep copy of the state before every transaction to allow for gas refunds/reverts upon failure.
   Solution: Introduced a StateJournal proxy dictionary in minichain/state.py. It acts as an in-memory cache that tracks diffs during transaction execution in O(1) time.
   Impact: If a transaction fails mid-execution (e.g., out of gas), the journal simply discards the cache (rollback()). If it succeeds, the diff is flushed to the backing dictionary (commit()), completely eliminating the need for transaction-level deep copies.
2. Block-level In-Memory Snapshots
   Problem: During a chain reorganization (resolve_conflicts), the node had to fetch the genesis state and sequentially re-apply every single transaction in history up to the fork point.
   Solution: Implemented _state_snapshots in minichain/chain.py (an OrderedDict limited to the 10 most recent blocks).
   Impact: When a shallow reorg occurs, the node now fast-forwards the difficulty/timestamp calculations and restores the exact state at the fork point directly from memory. Replaying from genesis is now strictly a fallback mechanism for incredibly deep reorgs.

Screenshots/Recordings:

TODO: If applicable, add screenshots or recordings that demonstrate the interface before and after the changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 20d148e and 4e3387a.

📒 Files selected for processing (2)

• minichain/chain.py
• minichain/state.py

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[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
minichain
block.py	92	16	83%	11, 15, 18–24, 73, 138–140, 165, 170, 179, 181
chain.py	210	52	75%	17, 22, 28, 32, 35, 39, 66–71, 79–80, 87–88, 116–119, 153, 166–169, 179–180, 189–190, 193–194, 198–199, 231, 244, 252–260, 284–293, 303–304, 321
contract.py	154	81	47%	11–12, 15–20, 36–89, 124, 128, 136, 192–195, 215–216, 225–227, 234–235, 239–241, 249–250, 252–253, 258–259, 261–262, 264–265, 267–268, 270–271
mempool.py	65	16	75%	17–18, 32–34, 39–40, 42–43, 49–50, 56, 59–60, 67–69
mpt.py	14	3	79%	18–20
p2p.py	263	196	25%	30–31, 71, 74, 77, 80, 83–90, 93–94, 97–98, 103, 118, 121, 124–126, 129–131, 134, 137, 140, 144–145, 155–157, 168–182, 189–195, 204–258, 263–373
persistence.py	171	39	77%	84, 90, 92, 133, 143–144, 223–224, 244, 247–248, 270, 282–293, 296–297, 303–307, 310–313, 316–320
pow.py	41	14	66%	28, 36, 46–48, 52–54, 64, 69–73
rpc.py	82	26	68%	41–42, 45, 61, 64, 68, 73–76, 78–91, 96–98
state.py	214	17	92%	35, 56–57, 90, 109–110, 156, 169, 217, 277, 302, 332, 335–340
validators.py	9	1	89%	13
TOTAL	1421	461	68%

Tests	Skipped	Failures	Errors	Time
76	0 💤	0 ❌	0 🔥	8.506s ⏱️