SDKs send queue is no longer shutdown immediately on re-init

[adinauer]

📜 Description

SDKs send queue is no longer shutdown immediately on re-init

💡 Motivation and Context

When re-initializing the SDK, we were:

• shutting down the queue immediately
• no longer allow enqueueing new items
• only added the current item in the queue to the offline cache (if available)
• discard the other items in the queue

This caused events to be lost in case of re-init, which is common in e.g. Spring Boot + Logback setups.

After the change we are:

• no longer allowing new items to be enqueued
• items in the queue will be processed until completion

💚 How did you test it?

📝 Checklist

• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[github-actions]

🚨 Detected changes in high risk code 🚨

High-risk code has higher potential to break the SDK and may be hard to test. To prevent severe bugs, apply the rollout process for releasing such changes and be extra careful when changing and reviewing these files:

• sentry/src/main/java/io/sentry/transport/AsyncHttpTransport.java

[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

- SDKs send queue is no longer shutdown immediately on re-init ([#4564](https://github.com/getsentry/sentry-java/pull/4564))

If none of the above apply, you can opt out of this check by adding #skip-changelog to the PR description.

Generated by 🚫 dangerJS against 7cbb0cc

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	456.60 ms	505.83 ms	49.23 ms
Size	1.58 MiB	2.09 MiB	519.47 KiB

Previous results on branch: feat/sdk-re-init-queue-drain

Startup times

Revision	Plain	With Sentry	Diff
5dff751	402.70 ms	471.67 ms	68.97 ms

App size

Revision	Plain	With Sentry	Diff
5dff751	1.58 MiB	2.09 MiB	519.03 KiB

[github-actions]

🚨 Detected changes in high risk code 🚨

High-risk code has higher potential to break the SDK and may be hard to test. To prevent severe bugs, apply the rollout process for releasing such changes and be extra careful when changing and reviewing these files:

• sentry/src/main/java/io/sentry/transport/AsyncHttpTransport.java

[github-actions]

🚨 Detected changes in high risk code 🚨

High-risk code has higher potential to break the SDK and may be hard to test. To prevent severe bugs, apply the rollout process for releasing such changes and be extra careful when changing and reviewing these files:

• sentry/src/main/java/io/sentry/transport/AsyncHttpTransport.java