Add CSL helpers for pooled mint outputs and tx chaining

[Nebyt]

Summary

• Extract a shared coinsPerUtxoByte / getDataCost so min-ada and the tx builder cannot drift.
• Add MintBuilder helpers, CIP-68 datum construction, and local UTxO chaining for follow-up mint txs.

Stack

• Base: feat/token-batch-plan (merge that PR first)
• Depends on: stacked on token-batch-plan so the mint UI PR can sit on both. This diff does not import the planner.
• Follow-up PR: TokenTab + tokenBatchMint

Test plan

• Review helpers against existing getTxBuilder min-ada usage
• Confirm no pool-id / stake-delegation changes are in this diff

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