73. Array.prototype.filter (Polyfill)

Implement Array.prototype.myFilter — a polyfill that behaves like native Array.prototype.filter.

Filter creates a new array containing all elements for which the callback returns a truthy value.

Requirements

1) Core behavior

• Return a new array.
• Invoke callbackFn for each existing element (skip holes).
• Callback signature: (value, index, array).
• Preserve original order of kept elements.
• Support optional thisArg for callbackFn.

2) Edge cases

• Throw TypeError if callbackFn is not a function.
• Capture the array length at start (pushes beyond original length are not visited).
• Sparse arrays: skip holes (missing indices) entirely.