change signatures to cosi

[TychoVrahe]

This PR simplifies image_validation and only leaves custom, CoSi based signatures.

Dev keys are hardcoded for now.

[Copilot]

Pull Request Overview

This PR updates the image validation signatures to use a custom CoSi-based implementation by replacing previous signature mechanisms with Trezor-crypto’s ed25519-donna sources and by hardcoding development keys for the time being.

• Added several new Trezor-crypto source files in boot/zephyr/CMakeLists.txt.
• Updated boot/bootutil/zephyr/CMakeLists.txt to include the new Trezor-crypto directory.
• Added a new file in boot/bootutil/trezor-crypto containing a relative path reference.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
boot/zephyr/CMakeLists.txt	Introduced new source files for Trezor-crypto and disabled precomputation for Ed25519.
boot/bootutil/zephyr/CMakeLists.txt	Added an include directory pointing to the Trezor-crypto sources.
boot/bootutil/trezor-crypto	Added a file with a relative path reference to the crypto directory.

Comments suppressed due to low confidence (1)

boot/bootutil/zephyr/CMakeLists.txt:12

• Ensure that the relative path '../trezor-crypto' correctly resolves to the intended directory across all build configurations to prevent potential include path issues.

+  ../trezor-crypto

[hiviah]

All requested changes are mostly documentation-wise since we will rely on this to be readable.