Function isSymbol

isSymbol(u: unknown): u is symbol
Type guard that checks if a value is a symbol.

Type Narrowing Behavior:
- Narrows unknown to symbol when true
- Identifies values created with Symbol() constructor
Parameters
- u: unknown
  The value to check
Returns u is symbol
true if u is a symbol, false otherwise. When true, TypeScript narrows the type to symbol.
Example
```
const id = Symbol('id');
const shared = Symbol.for('shared');
const tokens: unknown[] = [id, 'shared', shared];

const symbols = tokens.filter(isSymbol);

assert.deepStrictEqual(symbols, [id, shared]);
```
- Defined in src/guard/is-type.mts:278