Add polyfills for Convert.ToHexString[Lower](...) and Convert.FromHexString(...)

[Tyrrrz]

No description provided.

[Copilot]

Pull request overview

This PR adds polyfills for hexadecimal string conversion methods from the Convert class, enabling these .NET 5.0 and .NET 9.0 APIs to be used in earlier framework versions.

• Implements Convert.FromHexString, Convert.ToHexString (NET 5.0 APIs)
• Implements Convert.ToHexStringLower (NET 9.0 APIs)
• Includes comprehensive test coverage for the new polyfills

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
PolyShim/Signatures.md	Updated documentation to include 5 new Convert methods with correct version annotations
PolyShim/Net50/Convert.cs	Implements FromHexString and ToHexString polyfills with custom hex conversion logic using bitwise operations
PolyShim/Net90/Convert.cs	Implements ToHexStringLower by delegating to ToHexString and applying ToLowerInvariant()
PolyShim.Tests/Net50/ConvertTests.cs	Adds tests for hex string encoding/decoding including error cases for invalid input
PolyShim.Tests/Net90/ConvertTests.cs	Adds tests for lowercase hex string conversion with various input scenarios

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (b8db144) to head (823aa9f).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@     Coverage Diff      @@
##   master   #59   +/-   ##
============================
============================

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.