Update JaCoCo coverage badge

[github-actions]

Automated JaCoCo coverage badge update from CI.

[edburns]

@copilot whoa. Why the dramatic drop in code coverage? There was a huge drop in generated. Also, why the re-added "merged" badge? We broke out the badges into two buckets a while ago.

[Copilot]

@copilot whoa. Why the dramatic drop in code coverage? There was a huge drop in generated. Also, why the re-added "merged" badge? We broke out the badges into two buckets a while ago.

Addressed in 326dac6.

• I removed merged badge generation and deletion is now enforced in the badge script, so only handwritten/generated badges are produced.
• The generated percentage drop is from current JaCoCo data (not a badge calc bug): generated coverage is now being computed over com.github.copilot.sdk.generated*, and many newly generated RPC/event classes are currently at 0% instruction coverage, which pulls the aggregate down.