Function getYear

getYear(date: number | Date): number
Get the full year of the given date.

This function validates arguments before processing and returns the full year (e.g., 2025) of the given date. Returns NaN for invalid input.
Parameters
- date: number | Date
  The base date as a Date object or timestamp (number)
Returns number
The year as a number, or NaN if invalid
Example
```
// Get year from Date object
const result = getYear(new Date(2025, 0, 15));
// Returns: 2025

// Get year from timestamp
const result2 = getYear(1704067200000); // 2024-01-01
// Returns: 2024

// Leap year
const result3 = getYear(new Date(2024, 1, 29));
// Returns: 2024

// Historic date
const result4 = getYear(new Date(1776, 6, 4));
// Returns: 1776

// Invalid date returns NaN
const result5 = getYear(new Date("invalid"));
// Returns: NaN
```
Remarks
- Validates arguments before conversion (consistent with library patterns)
- Accepts both Date objects and numeric timestamps
- Returns NaN for: Invalid Date, NaN, Infinity, -Infinity
- Returns the year in the local timezone
- Supports negative years (BC dates)
- Defined in getYear/index.ts:42