fix nil pointer panic & make system routines more resilient against panics

[pk910]

Fix for a nil pointer panic from the system contract indexers when processing requests before the validator set is fully loaded:

time="2025-01-21T14:53:15Z" level=error msg="uncaught panic in WithdrawalIndexer.runWithdrawalIndexerLoop subroutine: runtime error: invalid memory address or nil pointer dereference, stack: goroutine 4901 [running]:
runtime/debug.Stack()\n\t/opt/hostedtoolcache/go/1.22.10/x64/src/runtime/debug/stack.go:24 +0x5e
github.com/ethpandaops/dora/utils.HandleSubroutinePanic({0x1502234, 0x2a})
  /home/runner/work/dora/dora/utils/process.go:20 +0xe5\npanic({0x1352e00?, 0x363fe30?})\n\t/opt/hostedtoolcache/go/1.22.10/x64/src/runtime/panic.go:770 +0x132
github.com/ethpandaops/dora/indexer/execution.(*WithdrawalIndexer).parseRequestLog(0xc0088fd3b0, 0xc009d780b0, 0xc00c354a88)
  /home/runner/work/dora/dora/indexer/execution/withdrawal_indexer.go:175 +0x1ee
github.com/ethpandaops/dora/indexer/execution.(*WithdrawalIndexer).processRecentTx(0xc0088fd3b0, 0xc009d780b0, 0xc00a21c1c0, 0xc0101ac508, {0xea, 0xdd, 0xb5, 0xdc, 0x21, 0xab, ...}, ...)
  /home/runner/work/dora/dora/indexer/execution/withdrawal_indexer.go:133 +0x90
github.com/ethpandaops/dora/indexer/execution.(*contractIndexer[...]).processRecentBlocksForFork(0x2d625c0, 0xc00c354a80)
  /home/runner/work/dora/dora/indexer/execution/contract_indexer.go:517 +0xfa3
github.com/ethpandaops/dora/indexer/execution.(*contractIndexer[...]).processRecentBlocks(0x2d625c0)
  /home/runner/work/dora/dora/indexer/execution/contract_indexer.go:345 +0x89
github.com/ethpandaops/dora/indexer/execution.(*contractIndexer[...]).runContractIndexer(0x2d625c0)
  /home/runner/work/dora/dora/indexer/execution/contract_indexer.go:132 +0xb1
github.com/ethpandaops/dora/indexer/execution.(*WithdrawalIndexer).runWithdrawalIndexerLoop(0xc0088fd3b0)
  /home/runner/work/dora/dora/indexer/execution/withdrawal_indexer.go:100 +0x85
created by github.com/ethpandaops/dora/indexer/execution.NewWithdrawalIndexer in goroutine 1
  /home/runner/work/dora/dora/indexer/execution/withdrawal_indexer.go:82 +0x4d6
" error="runtime error: invalid memory address or nil pointer dereference"

This PR also add an automatic restart for important system routines on panics.