feat: Span v2 Envelopes

[jamescrosswell]

Partially implements #4790:

• Implement Span-First #4790

[github-actions]

Semver Impact of This PR

⚪ None (no version bump detected)

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---

Features ✨

• feat: Span v2 Envelopes by jamescrosswell in #4912

Dependencies ⬆️

• chore(deps): Bumped Xamarin.AndroidX.Lifecycle.Common.Java8 and CommunityToolkit.Mvvm to 2.2.20 and 8.4.0 by jamescrosswell in #4876

---

_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

	Fails
🚫	Please consider adding a changelog entry for the next release.

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Instructions and example for changelog

Please add an entry to CHANGELOG.md to the "Unreleased" section. Make sure the entry includes this PR's number.

Example:

## Unreleased

### Features

- Span v2 Envelopes ([#4912](https://github.com/getsentry/sentry-dotnet/pull/4912))

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Generated by 🚫 dangerJS against fc0cebc

[codecov]

Codecov Report

❌ Patch coverage is 72.09302% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.84%. Comparing base (f95f266) to head (fc0cebc).

Files with missing lines	Patch %	Lines
src/Sentry/Protocol/SpanV2.cs	68.49%	21 Missing and 2 partials ⚠️
src/Sentry/Protocol/Envelopes/Envelope.cs	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4912      +/-   ##
==========================================
+ Coverage   73.88%   76.84%   +2.96%     
==========================================
  Files         494      406      -88     
  Lines       17868    15156    -2712     
  Branches     3509     3025     -484     
==========================================
- Hits        13202    11647    -1555     
+ Misses       3807     2791    -1016     
+ Partials      859      718     -141     

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