feat: electra withdrawals

[LeanSerra]

Motivation

Implement changes in Electra to withdrawals + fix all spec-tests related to it.

Description

• Modified get_expected_withdrawals link
• Modified process_withdrawals link

Fixed Spec Tests

test/generated/mainnet/electra/operations.exs:
previous: 333 tests, 19 failures
now: 333 tests, 0 failures

test/generated/mainnet/electra/sanity.exs:
previous: 97 tests, 8 failures, 1 skipped
now: 97 tests, 2 failures, 1 skipped

test/generated/minimal/electra/operations.exs:
previous: 366 tests, 38 failures
now: 366 tests, 0 failures

test/generated/minimal/electra/sanity.exs:
previous: 104 tests, 8 failures, 1 skipped
now: 104 tests, 2 failures, 1 skipped

tests fixed: 69

Spec Test Progress

11370 tests, 4 failures, 784 skipped