Add hard-coded Version.cs for telemetry

[kailash-b]

✏️ Changes

This PR makes the SDK version reported in the Auth0-Client telemetry header explicit and release-managed, instead of deriving it from assembly reflection.

The version is now sourced from a hard-coded constant that release automation bumps on every release, matching

Added

• Version.cs — internal static class Version exposing Current ("1.0.0-beta.6"), the single constant used for telemetry.

Modified

• Utils.CreateAgentString() — now builds the agent string from Version.Current instead of assembly reflection. Removed the System.Reflection import and the stale doc comment.
• UtilsTests.cs — the name/version assertion now checks against Version.Current exactly rather than a loose regex.

Removed

• Utils.BuildVersionString(Version?) — no longer needed once reflection is gone.
• The BuildVersionString and assembly-null-fallback unit tests that covered it.

🔗 References

🎯 Testing

• Full unit suite passes locally (610 passed, 0 failed).

• This change adds unit test coverage

• This change adds integration test coverage - N/A, telemetry header content is covered by unit tests.

• This change has been tested on the latest version of the platform/language or why not

✅ Checklist

• I have read the Auth0 general contribution guidelines

• I have read the Auth0 Code of Conduct

• All existing and new tests complete without errors

• All commits are signed.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.50%. Comparing base (61ffe19) to head (64f751a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
- Coverage   92.53%   92.50%   -0.04%     
==========================================
  Files          29       29              
  Lines        1433     1427       -6     
  Branches      164      163       -1     
==========================================
- Hits         1326     1320       -6     
  Misses         76       76              
  Partials       31       31              

☔ View full report in Codecov by Harness.
📢 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.