fix(txbuilder): allow native-script DRep certificates without a redeemer

[emmanuel-musau]

Why this PR is more than the requested test

Follow-up to #432. The review asked for a devnet test with mixed Plutus and
native-script voters in one transaction (using governance_voting.ak).

Writing that test surfaced a blocker: before a native-script DRep can vote on
devnet, it has to be registered, and TxBuilder rejected the registration
with "Redeemer required for script-controlled DRep credential registration".

The fix

Mirrors the approach from #432, deferring the native-vs-Plutus decision to
build time:

• Removed the eager "redeemer required" failures from
  createRegisterDRepProgram, createUpdateDRepProgram, and
  createDeregisterDRepProgram.
• Added a validateCertRedeemers build-time pass,
  run alongside validateVoterRedeemers. It classifies
  the DRep credential's script via .attachScript() or reference inputs:
  Plutus credentials still require a redeemer (with guidance in the error for
  both cases); native-script credentials need none, and a mistakenly supplied
  redeemer is pruned with a debug log.
• Extracted the script classifier shared with the voter pass into
  makeIsNativeScript rather than duplicating it.

Tests

• TxBuilder.NativeScriptDRepCert.test.ts unit coverage of the cert paths
  (fail without the fix, pass with it).
• TxBuilder.MixedVoters.test.ts the requested devnet test: one transaction
  with a Plutus DRep voter (keeps its redeemer) and a native-script DRep voter
  (redeemer pruned), registered end-to-end and accepted by the ledger.

[emmanuel-musau]

Related: #448 — the same eager-redeemer defect exists for CC cold credentials (authCommitteeHot / resignCommitteeCold).
There is an issue open for this check it and confirm.