Add border and drawing primitives (lines, circles) to image manipulation API

[Copilot]

Extends the library with two commonly needed capabilities: adding borders/padding to images and drawing basic geometric primitives.

Border Methods

• border(width, r, g, b, a) - uniform border on all sides
• borderSides(top, right, bottom, left, r, g, b, a) - asymmetric borders
• Increases dimensions accordingly, preserves metadata (DPI, physical dimensions)

Drawing Primitives

• drawLine(x0, y0, x1, y1, r, g, b, a) - Bresenham's algorithm for pixel-perfect lines
• drawCircle(cx, cy, radius, r, g, b, a, filled) - Midpoint circle algorithm with fill option
• Automatic bounds clipping, RGBA support including transparency

Example

const canvas = Image.create(400, 300, 255, 255, 255);

// Draw shapes
canvas
  .drawCircle(100, 100, 50, 255, 0, 0, 255, true)  // filled red circle
  .drawLine(0, 0, 400, 300, 0, 0, 255)              // blue diagonal
  .border(20, 0, 0, 0);                              // 20px black border

await Deno.writeFile("output.png", await canvas.encode("png"));

All methods follow the chainable API pattern. Test coverage: 18 new tests, 393 total passing.

Original prompt

Identify and implement the two best new features for the library. Consider both extending existing features of adding new.

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