feat: @metamask/delegation-core encoders and decoders now accept periodDuration as bigint

[jeffsmale90]

📝 Description

MultiTokenPeriod, NativeTokenPeriodTransfer and Erc20TokenPeriodTransfer enforcers encode periodDuration as UINT256. Because number is the natural type for duration represented as seconds, it was chosen as the periodDuration type for the typescript interface.

There's a case where the enforcer is used to encode a single allowance, where the period duration is simply set as UINT256_MAX - meaning there's no real possibility of a second duration (unless you wait ~3.6 times 10^69 years).

By making the config type generic with default value, the return type of decodeXXX is unchanged, and a caller can specify periodDuration as bigint.

🧪 How to Test?

This is a typing only change, as the encoders already work with periodDuration values specified as bigint. New unit tests invoke the encodeXXX functions with periodDuration as bigint.

⚠️ Breaking Changes

Non breaking.

List any breaking changes:

• No breaking changes
• Breaking changes (describe below):

📋 Checklist

Check off completed items:

• Code follows the project's coding standards
• Self-review completed
• Documentation updated (if needed)
• Tests added/updated
• Changelog updated (if needed)
• All CI checks pass

🔗 Related Issues

Link to related issues:
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📚 Additional Notes

Any additional information, concerns, or context:

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Note

Low Risk
Low risk typing/API-surface tweak: encoding already uses uint256 and runtime behavior is unchanged; primary impact is TypeScript types and added test coverage.

Overview
Adds bigint support for periodDuration inputs in the MultiTokenPeriod, ERC20TokenPeriodTransfer, and NativeTokenPeriodTransfer terms/encoder APIs by making the term types generic and widening the encoder overloads to number | bigint.

Keeps decode output unchanged (still decoding periodDuration to a number), and adds unit tests to ensure encoding accepts bigint durations and decoding normalizes them back to numbers. The CHANGELOG.md is updated to document the behavior change.

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