Fix: Make second parameter of Mat.ucharPtr optional

[Copilot]

The Mat.ucharPtr method's second parameter j should be optional to support getting row data by passing only the row index, as indicated in the TypeScript method signature and OpenCV documentation.

Problem:
The current type definition required both parameters:

public ucharPtr(i: any, j: any): any;

This prevented developers from calling ucharPtr with just a row index to get a pointer to the entire row, which is a valid and commonly used pattern in OpenCV.

Solution:
Made the second parameter optional:

public ucharPtr(i: any, j?: any): any;

Usage:

const mat = new cv.Mat(3, 3, cv.CV_8UC1);

// Get pointer to entire row (now works)
const rowPtr = mat.ucharPtr(0);

// Get pointer to specific element (still works)
const elementPtr = mat.ucharPtr(0, 0);

This change makes the TypeScript definitions consistent with the actual OpenCV.js implementation and allows the more flexible usage pattern that developers expect.

Fixes #82.

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