feat: use log id for interop root indexing

[Artemka374-claude]

Summary

Replaces the compound InteropRootsLogIndex (block number + index-in-block) with a plain u64 log ID (totalPublishedInteropRoots counter from the IMessageRoot contract) everywhere interop root indexing was used.

• InteropRootsLogIndex is removed from all live codepaths (mempool, sequencer, storage, block context provider, interop watcher). It is kept only for backward-compat with the v1 and v2 network wire format.
• The interop watcher now uses a binary search over MessageRoot.totalPublishedInteropRoots to find the correct starting L1 block, replacing the previous approach of storing the block number directly.
• SystemTxEnvelope::import_interop_roots now takes log_id as an explicit salt to ensure transaction uniqueness.
• The RocksDB WAL column family is renamed from starting_interop_event_index to starting_interop_root_id (note: existing DBs will not have this column and will fall back to 0).

This PR is the clean rebased replacement for the outdated merge-follow-up flow from #1092 / #1142.

Testing

• cargo nextest run --workspace --exclude zksync_os_integration_tests
• PATH="$HOME/.foundry/bin:$PATH" cargo nextest run -p zksync_os_integration_tests --profile no-pig