Replaced reorg detection with parent hash verification

[yug49]

Resolves #214

Description

Refactors reorg detection from on-chain hash existence checks to parent hash verification against a ring buffer.

Changes

• ring_buffer.rs: Added BlockInfo<H> struct storing block number + hash, with find_by_number() and truncate_from() methods
• reorg_handler.rs: Replaced hash existence checks with parent hash verification; added handle_gap() for intermediate block fetching

Scenarios

Scenario	Before	After
Direct reorg (1→2→3→REORG→2)	3 RPC calls	0 RPC calls
Block past fork (1→2→3→(2 reorged)→3)	3 RPC calls	1 RPC call
Gap with reorg (1→2→3→(6 reorged)→8)	1 RPC call	5 RPC calls (but maintains fuller buffer)

Edge cases handled

• Empty buffer (first block)
• Reorg deeper than buffer size → fallback to finalized block
• Gaps in block numbers → fetch intermediate blocks

[0xNeshi]

Hey @yug49 thanks for contributing!
Our team is currently working though some priority items, so we'll get to reviewing this as soon as our schedule allows.
We appreciate your patience and the contribution!

[yug49]

Sure, it was my pleasure to contribute