Function isNumber

isNumber(u: unknown): u is number
Type guard that checks if a value is a number.

Type Narrowing Behavior:
- Narrows unknown to number when true
- Includes NaN, Infinity, and -Infinity as valid numbers
- Preserves literal number types when possible
Parameters
- u: unknown
  The value to check
Returns u is number
true if u is a number, false otherwise. When true, TypeScript narrows the type to number.
Example
```
const mixed: unknown[] = [1, '2', 3];

const numbers = mixed.filter(isNumber);

assert.deepStrictEqual(numbers, [1, 3]);
```
- Defined in src/guard/is-type.mts:125