V3 - Use BPP from Color Writer for Compressor

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

Uses the computed BitsPerPixel from the color writer instance for the compressor to ensure parity.

Fixes #2909

[Copilot]

Pull Request Overview

This PR updates the TIFF compressor initialization to use the computed BitsPerPixel from the color writer, ensuring parity between the compressor and the color writer. Key changes include:

• Defining a new test image constant for Issue2909.
• Adding new test cases for LZW and Deflate compression using the Issue2909 file.
• Updating the TiffEncoderCore to obtain BitsPerPixel from the color writer instead of from the encoder instance.

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/ImageSharp.Tests/TestImages.cs	Added constant for Issue2909 test image.
tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderTests.cs	Added test cases for LZW and Deflate compression using Issue2909.
src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs	Changed compressor initialization to use colorWriter.BitsPerPixel.

Files not reviewed (1)

• tests/Images/Input/Tiff/Issues/Issue2909.tiff: Language not supported