fix(session): Fix bitmap stride mismatch and out-of-bounds writes for xRDP compatibility

[Amartya Anshuman (amartyaa)]

Fixes #1251

Summary

This PR fixes two related issues in ironrdp-session that cause diagonal bitmap distortion and index-out-of-bounds panics when connecting to xRDP servers.

Changes

crates/ironrdp-session/src/fast_path.rs

xRDP sends bitmap updates where the data dimensions (update.width × update.height) differ from the destination rectangle (update.rectangle). Per MS-RDPBCGR §2.2.9.1.1.3.1.2.2, bitmapWidth/bitmapHeight define the pixel data layout while destLeft/destTop/destRight/destBottom define the screen placement.
The apply_* methods use the rectangle's width as the row stride. Passing update.rectangle when it's wider/narrower than the actual data causes diagonal shearing.
Fix: Construct a blit_rect whose dimensions match the actual bitmap data, positioned at the destination's top-left corner:

let blit_rect = InclusiveRectangle {
    left: update.rectangle.left,
    top: update.rectangle.top,
    right: update.rectangle.left + update.width.saturating_sub(1),
    bottom: update.rectangle.top + update.height.saturating_sub(1),
};

crates/ironrdp-session/src/image.rs

Added bounds checks to all apply_* bitmap methods that were missing them:

• apply_rgb16_bitmap
• apply_rgb15_bitmap
• apply_bgr24_bitmap
• apply_rgb8_with_palette
• apply_rgb24_iter
• apply_rgb32_bitmap (both same-format and cross-format paths)
• data_for_rect (clamped to buffer length)

Each pixel write is now guarded with if dst_idx + bytes_per_pixel < self.data.len().
This is consistent with how other parts of the codebase handle edge-of-framebuffer updates — pixels beyond the buffer are silently clipped rather than panicking.

Also added a max_rows clamp in apply_rgb24_iter to prevent iterating beyond the framebuffer height.

Testing

• Tested against xRDP 0.10.x (Ubuntu 22.04, Xorg session with XFCE)
• Verified correct rendering at 8bpp, 15bpp, 16bpp, 24bpp, and 32bpp
• No more diagonal distortion on the xRDP login screen or desktop
• No more panics during session startup or bitmap updates near framebuffer edges
• Verified no regression when connecting to Windows RDP servers (Windows 10/11)