Move SELFDESTRUCT/SystemAddress BAL tests to the engine-API tester

Summary

Test-only refactor. Moves the three EIP-7928 SELFDESTRUCT-beneficiary BAL
regression tests from execution/execmodule/bal_selfdestruct_systemaddress_test.go
(driven by blockgen.GenerateChain — proposer/assembler path only) into
execution/engineapi/engine_api_bal_test.go, where they run through the full
engine BuildCanonicalBlock round-trip (serial proposer and parallel
validator via newPayload). No production code changes.

These tests guard the regression fixed in #21333: per EIP-7928 a SELFDESTRUCT
records the beneficiary as a state access independent of any value transfer, and
the SYSTEM_ADDRESS carve-out keeps that entry because the SELFDESTRUCT is itself
the access. Pre-fix, a zero-balance SELFDESTRUCT to SYSTEM_ADDRESS dropped the
BAL entry → BAL hash mismatch → block rejected / sync stall.

Changes

• Add to execution/engineapi/engine_api_bal_test.go:
  • TestEngineApiBALIncludesSystemAddressOnSelfdestructToItWithZeroBalance — the
    bug scenario: CREATE tx with init code PUSH20 SYSTEM_ADDRESS; SELFDESTRUCT
    and zero contract balance. Asserts the BAL contains a SystemAddress entry
    with every change-set empty.
  • TestEngineApiBALIncludesSystemAddressOnSelfdestructToItWithNonZeroBalance —
    guard: same init code, 1 wei sent to the contract; asserts a balance change on
    the SystemAddress entry.
  • TestEngineApiBALIncludesOrdinaryBeneficiaryOnSelfdestructWithZeroBalance —
    guard: an ordinary EOA beneficiary (carve-out N/A) still appears in the BAL.
  • Helpers newSelfdestructBALTester, signCreateTx, pushAddrSelfdestruct.
• Delete execution/execmodule/bal_selfdestruct_systemaddress_test.go.

Notes

• Consistent with the existing BAL tests in the file: each is gated with
  if !dbg.Exec3Parallel { t.Skip("requires parallel exec") } and runs under
  ERIGON_EXEC3_PARALLEL=true (the BAL is only produced under parallel exec).
• A node accepts its own BAL, so BuildCanonicalBlock stays VALID even pre-fix
  (proposer and validator compute the same wrong BAL). The regression is caught
  by asserting BAL contents (the missing SystemAddress entry), not a
  payload-INVALID status.

Test plan / TDD verification

ERIGON_EXEC3_PARALLEL=true go test -count=1 -run TestEngineApiBALIncludes ./execution/engineapi/

The red/green split (only the zero-balance SystemAddress case fails) matches
#21333's own TDD note — the bug is specific to SYSTEM_ADDRESS + zero balance.

• golangci-lint on execution/engineapi/... and execution/execmodule/...: 0 issues.