feat(events): replace symbolic execution with structural classify-resolve pipeline

Replace the old multi-round symbolic execution engine with a two-phase
Classify→Resolve pipeline for event selector extraction.

Phase 1 (Classify): Build CFG, collect LOG sites, run single-block symbolic
execution to determine topic0 source type (Push32/PushN/MloadCodecopy/CrossBlock).

Phase 2 (Resolve): Extract event hashes per class — direct bytecode read for
Push32/PushN, CODECOPY argument analysis for MloadCodecopy, BFS backward
traversal through predecessor blocks for CrossBlock.

Additional improvements:
- ContinuationCache + BlockStateCache for CrossBlock resolution
- Precise CODECOPY resolver with size=32 validation
- Known non-event constants blocklist (27 entries, e.g. role hashes, EIP-712)
- Forward reachability validation using function entry contexts

Code reduced from ~5,700 lines to ~950 lines.

Author: qdzzyb2014