feat: Send transactions as Span v2 streams

[jamescrosswell]

Partially implements #4790:

• Implement Span-First #4790

[github-actions]

Semver Impact of This PR

⚪ None (no version bump detected)

📋 Changelog Preview

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---

Features ✨

• feat: Send transactions as Span v2 streams by jamescrosswell in #4912

Dependencies ⬆️

Deps

• Apps built using the Sentry SDK for .NET must now target iOS version 15 or higher. Previously only version 13 or higher was required. (#4781) by github-actions in #4781
• Bump Cocoa SDK from v8.57.3 to v9.2.0 (#4781) by github-actions in #4781
  • changelog
  • diff
• chore(deps): update Native SDK to v0.12.7 by github-actions in #4920

Other

• test(android): Use volatile to produce SIGSEGV in native crash test by jpnurmi in #4919

---

_{🤖 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

- Send transactions as Span v2 streams ([#4912](https://github.com/getsentry/sentry-dotnet/pull/4912))

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[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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[jamescrosswell]

@Flash0ver just a heads up, I needed Attributes for the span streaming stuff so extracted this functionality out from the SentryMetrics class... just in case you might change any of this in another PR.