Multi-Contract Event Watcher

Queries every contract in your list as a single log filter rather than one scan each, so watching ten costs about what watching one does — that efficiency is the entire argument for a multi-contract watcher. Any event signature works, with shortcuts for the common ones, and an optional filter on the first indexed argument narrows to a particular sender or owner. Results are grouped by contract with counts, share of total and the block range each was active over, and decoded arguments for the most recent matches. It also reports which of the watched contracts produced nothing at all, which is frequently the more useful half of the answer. Block ranges are chunked and back off automatically, because every RPC caps them differently and a single refusal should not end the scan.