Function RI64

RI64(): TRI64
Creates a schema for signed 64-bit integers using JavaScript BigInt.

Use for large signed integers that exceed JavaScript's safe integer range (±2^53-1).

Returns TRI64
A Relish schema for i64 values
Example
```
import { RI64, createCodec } from '@grounds/schema';

const codec = createCodec(RI64());
codec.encode(BigInt('-9007199254740992')).match(
  (bytes) => console.log('I64 encoded:', bytes),
  (error) => console.error(error)
);
```
See
- RI32 for 32-bit signed
- RI128 for 128-bit signed