V4 - Use BPP from Color Writer for Compressor

[JimBobSquarePants]

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Description

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

Fixes #2909

[Copilot]

Pull Request Overview

This PR ensures that the compressor uses the calculated BitsPerPixel from the Color Writer, aligning the encoder behavior with the computed image properties.

• Added a constant for Issue2909 in the test images.
• Introduced two new tests verifying LZW and Deflate compressions using the Issue2909 test image.
• Refactored the TiffEncoderCore compressor creation to use colorWriter.BitsPerPixel instead of an external bitsPerPixel value.

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 a new constant for Issue2909 test image reference.
tests/ImageSharp.Tests/Formats/Tiff/TiffEncoderTests.cs	Added new tests for LZW and Deflate compression support.
src/ImageSharp/Formats/Tiff/TiffEncoderCore.cs	Refactored compressor instantiation to use the color writer’s BitsPerPixel.

Files not reviewed (1)

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