Resolve Type Inconsistencies in 64-bit Validators and Write Functions

[merlindiavova]

Problem Summary

The validator functions currently require bigint types, but in practice, I (and other developers) often pass number values to write functions like writeI64 and writeU64. This mismatch causes runtime errors and adds unnecessary friction.

Affected files:

• https://github.com/bare-ts/lib/blob/main/src/codec/primitive.ts
• https://github.com/bare-ts/lib/blob/main/src/util/validator.ts

Why This Matters

I would like the API to be intuitive and consistent. Right now, it's too easy to hit a runtime error when using numbers instead of BigInts, especially since we naturally reach for numbers for smaller values.

Proposed Solution: Dual-Type Support

Updating the validators and write functions to accept both bigint and number types. This approach reduces surprises and keeps the API simple and flexible.

Changes:

1. Update validators to handle both types:

export function isI64(val: bigint | number): boolean {
  // ...
}

2. Modify write functions to auto-convert numbers to BigInt:

export function writeU64(bc: ByteCursor, x: bigint | number): void {
  const bigIntValue = typeof x === 'bigint' ? x : BigInt(x);
  // ...
}

Additional Considerations

Documentation
Clearly document that writeI64/writeU64 now support both types, and reserve Safe versions for cases where number-only input is explicitly desired.

Testing
Add tests for mixed-type inputs to ensure stability across use cases.

Impact

• Breaking change? Mild, expanding signatures, not restricting them.
• Backward compatibility? Preserved, existing BigInt usage remains unchanged.

[merlindiavova]

If there are no major objections, I can go ahead create a PR.