feat(solana-exec): accurate tx volume via raw sig pagination

[Flotapponnier]

Summary

• Paginate all raw sigs from getSignaturesForAddress and count successful ones per hour bucket into a new solana_exec_raw_counts table — this gives accurate total trade volume without burning Helius enhanced API credits
• Cap enhanced API calls at 100 sigs/poll (fee quality sample, budget-safe: ~432K CUs/month on free tier vs 16M without the cap)
• Migration 002 adds solana_exec_raw_counts table and bumps tx_count to BIGINT
• Materialize now joins raw counts so tx_count reflects real volume, not just the 100-sig sample

Test plan

• Migration applied on VPS (done: CREATE TABLE, ALTER TABLE confirmed)
• Collector rebuilt and running without crash (done: no more enhanced batch max 100 sigs error)
• After next materializer run, check solana_exec_facts.tx_count shows real hourly volume (~4500 trades/hour for pump.fun)