[eth-rpc]: add resumable block sync and improve CLI arguments

[marian-radu]

Resumable block sync

• New block_sync module syncs backward from the latest finalized block to the first EVM block, with restart-safe checkpoint tracking via a sync_state SQLite table.
• On restart, fills only the top gap (new blocks) and bottom gap (remaining backfill) without re-syncing completed ranges.
• Auto-discovers and persists first_evm_block — the lowest block with EVM support on the chain.
• Chain identity verification: stores genesis hash in sync_state and validates on startup; detects stale boundaries after reorgs.

CLI rework

New --eth-pruning flag replaces --database-url, --cache-size, --index-last-n-blocks, and --earliest-receipt-block:

• --eth-pruning archive (default): persistent on-disk DB with backward historical sync.
• --eth-pruning <N>: in-memory DB keeping the latest N blocks.

CLI migration guide

Previous flag	Replacement	Notes
--cache-size N	--eth-pruning N	In-memory DB, keeps latest N blocks
--database-url sqlite::memory:	--eth-pruning N	--eth-pruning N always uses in-memory DB
--database-url /path/to/db.sqlite	--base-path /path/to/dir	Persistent DB stored as eth-rpc.db inside the directory
--index-last-n-blocks N	--eth-pruning archive	Syncs all finalized blocks down to the first EVM block
--earliest-receipt-block N	(removed)	Replaced by auto-discovered first_evm_block

Note: --dev automatically uses a temporary directory with an on-disk DB, which is deleted on exit.

Note: When --base-path is omitted, the DB is stored in the default OS data directory:

• macOS: ~/Library/Application Support/eth-rpc/
• Linux: ~/.local/share/eth-rpc/
• Windows: %APPDATA%\eth-rpc\

Examples

# Local dev node (on-disk DB in a temporary directory, deleted on exit)
eth-rpc --dev

# In-memory DB, keep only the latest 512 blocks
eth-rpc --node-rpc-url wss://example.com:443 --eth-pruning 512

# Persistent DB with historical sync (default, --eth-pruning archive is implicit)
eth-rpc --node-rpc-url wss://example.com:443

# Persistent DB with historical sync at a custom path
eth-rpc --node-rpc-url wss://example.com:443 --base-path /data/eth-rpc

# Explicit archive mode
eth-rpc --node-rpc-url wss://example.com:443 --eth-pruning archive

https://github.com/paritytech/contract-issues/issues/271

[paritytech-release-backport-bot]

Created backport PR for stable2603:

• [stable2603] Backport #11153 #11489 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-11153-to-stable2603
git worktree add --checkout .worktree/backport-11153-to-stable2603 backport-11153-to-stable2603
cd .worktree/backport-11153-to-stable2603
git reset --hard HEAD^
git cherry-pick -x 8c6f7606348edee72a7a1abf14807e38bec5ca17
git push --force-with-lease