Performance optimizations, improved UlidJsonConverter

[Seramis]

Description

Improved the MethodImpl attribute usage. Same performance but more logical line between inlining.
New implementation for IsValid method.
Restored implementation of Fill from version 1.3.5, which was faster and new benchmarks now can show that.
Improved UlidJsonConverter to not silently fail.
Updated README.md file with new benchmark data.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Other (please specify): Performance

Checklist

• The PR is submitted to the correct branch (main).
• My code follows the project's coding style. (.editorconfig)
• I have commented my code, particularly in hard-to-understand areas and public interfaces.
• I have added or updated tests for the changes I made.
• All new and existing tests passed.
• I have updated the documentation where applicable.