Improve beacon chain state download

[naddison36]

Summary

Improves beacon chain state downloads used by verifyBalances and verifyDeposits.

A production download stalled after receiving response headers, with no visibility into whether data was still being transferred. This change:

• Reads the response body in binary chunks.
• Reports downloaded bytes, percentage, and average speed every 10 seconds.
• Includes downloaded byte counts in timeout errors.
• Validates that the received body matches the advertised content length.
• Keeps the state in memory for proof generation.
• Removes beacon-state disk caching and the obsolete cleanup helper.

No smart contracts or deployment scripts are changed.

Testing

Ran verifyBalances locally in dry-run mode against mainnet and QuickNode:

DEPLOYER_PK=<development-key> \
pnpm exec tsx tasks/run.ts verifyBalances \
  --network mainnet \
  --dryrun

Observed a successful beacon state download and proof generation:

origin:utils:beacon Fetching state for slot 14943527 from the beacon node
origin:utils:beacon Received response headers for state at slot 14943527, downloading body
origin:utils:beacon Downloaded 334324589 bytes for state at slot 14943527

The approximately 319 MiB state downloaded locally in around 9 seconds.

Additional checks:

• JavaScript and TypeScript formatting
• JavaScript syntax validation
• Focused TypeScript lint