Remove support for varsig v0

[MichaelMure]

No description provided.

[Copilot]

Pull Request Overview

This PR removes support for varsig version 0 (v0), simplifying the codebase to only support version 1. The changes streamline the API by removing version-specific logic, signature validation, and related error handling for v0 compatibility.

Key changes:

• Removed all v0-specific encoding/decoding logic and validation
• Simplified constructor functions to no longer return errors or accept options
• Eliminated signature field support from the Varsig interface

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
varsig.go	Removes v0 support from core varsig struct, eliminates signature field and validation logic
varsig_test.go	Removes all v0-related test cases and validation scenarios
rsa.go	Simplifies RSA varsig constructor and removes v0-specific encoding logic
rsa_test.go	Removes v0 test cases and simplifies constructor calls
eddsa.go	Simplifies EdDSA varsig constructor and removes v0-specific logic
eddsa_test.go	Removes v0 test cases and updates constructor calls
ecdsa.go	Simplifies ECDSA varsig constructor and removes v0-specific logic
registry.go	Updates decode function signature and adds v1 version check
registry_test.go	Removes v0 test cases and updates test helper functions
option.go	Completely removes options system used for v0 compatibility
error.go	Removes v0-specific error types
constant.go	Simplifies payload encoding decoding by removing v0 logic
constant_test.go	Updates tests to remove v0-specific cases
common.go	Simplifies convenience functions to no longer return errors
common_test.go	Updates test cases to use simplified constructors