fix: preserve Map (and bigint) in cloneOutput via structuredClone

[OscarOzaine]

Summary

cloneOutput deep-cloned outputs via a JSON round-trip (JSONBig.parse(JSONBig.stringify(...))), which silently drops Map entries (and mangles bigint) inside a Mesh Data inline datum. When an inline datum contains a Map — e.g. CIP-68 metadata produced by metadataToCip68 and used with .txOutInlineDatumValue(..., "Mesh") — the Map was cloned to an empty {}, and serialization later threw TypeError: Cannot convert undefined to a BigInt in toPlutusData.

This switches cloneOutput to structuredClone, which preserves Map, bigint, Uint8Array and nested structures. It's also consistent with how the tx builder already clones txOutput and other queue items in tx-builder-core.ts.

Fixes #704

Root cause

packages/mesh-transaction/src/mesh-tx-builder/index.ts — cloneOutput is called by getOutputMinLovelace on every min-ADA calculation, so any output whose inline datum holds a Map was corrupted during transaction building.

// before
export const cloneOutput = (output: Output): Output => {
  return JSONBig.parse(JSONBig.stringify(output));
};
// after
export const cloneOutput = (output: Output): Output => {
  return structuredClone(output);
};

Tests

Adds packages/mesh-transaction/test/clone-output.test.ts:

• a Map inside a Mesh Data inline datum survives cloning (size + entries),
• bigint fields survive,
• the clone is a deep, independent copy,
• plain ADA-only outputs are unaffected.

All existing @meshsdk/transaction tests pass (24 suites / 128 tests); tsc --noEmit clean; prettier clean.

Credit

Thanks to @Daennes for the precise diagnosis and for suggesting structuredClone in the issue.

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