Cardano Updates

Replaces float-based lovelace arithmetic with BigInt throughout purchaseAsset
to avoid silent precision loss for NFT prices above Number.MAX_SAFE_INTEGER
(~9,007,199 ADA). The previous `as number` casts were TypeScript-only lies
that caused a TypeError at runtime; converting via Number() fixed the crash
but introduced silent rounding errors for large prices.

Changes:
- All fee and seller-payment calculations now use BigInt operators; quantities
  are only converted to string at the txOut boundary.
- Ceiling division implemented as (a * b + 9999n) / 10000n instead of
  Math.ceil(float), which is exact and matches the on-chain semantics.
- 1-ADA minimum fee floor is now guarded by priceBig > 0n so free listings
  (price = 0) no longer incur a spurious mandatory fee.
- lovelaceEntry guard replaces the !.quantity non-null assertion with a
  descriptive error instead of an opaque TypeError.
- Constructor validates feePercentageBasisPoint is in [0, 10000] and throws
  early rather than silently producing unbalanceable transactions.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

OfflineEvaluator.evaluateTx pushed resolved UTxOs into the caller's
additionalUtxos array (a surprising side effect that accumulated across
repeated calls) and fetched each parent transaction's UTxOs sequentially,
so latency scaled linearly with the number of distinct input transactions.

It now copies the input array and resolves distinct parent transactions
concurrently via Promise.all, leaving the caller's array untouched. The
two in-tree callers pass a freshly built array and read only the return
value, so behavior is unchanged for them.

Adds a no-mutation assertion to the existing evaluator test, which already
resolves inputs across several parent transactions (exercising the parallel
path).

Refs audit findings PERF-001, REL-003

Co-Authored-By: Claude Opus 4.8 <[email protected]>

cloneOutput used a JSON round-trip, which silently drops Map entries and
mangles bigint inside Mesh Data inline datums (e.g. CIP-68 metadata from
metadataToCip68). The empty Map then made serializeOutput throw
"Cannot convert undefined to a BigInt".

Use structuredClone, consistent with how the tx builder already clones
txOutput and other queue items in tx-builder-core.ts.

Adds regression tests for Map preservation, bigint preservation,
deep-copy independence, and plain ADA-only outputs.

Fixes #704

Co-Authored-By: Claude Opus 4.8 <[email protected]>