Remove deprecated Doppler recentLogs for 6.x

[jorbaum]

Follows up on #1181 / #1348.

• Remove DopplerClient.recentLogs(), RecentLogsRequest, Applications.logs(LogsRequest), and LogsRequest - deprecated in 5.x (feat: Replace deprecated Doppler recentLogs with Log Cache client 5.X.X #1348)
• Throw UnsupportedOperationException for deprecated logs() with recent==true

Note on default behavior

With recent changes in #1348logs(ApplicationLogsRequest) defaults to recent=true (LogCache) when recent is null. This differs from logs(LogsRequest), where null defaulted to recent=false (Doppler streaming).

┌──────────────┬────────────────────┬───────────────────┐
│ recent value │ Before #1348 │ After #1348. │
├──────────────┼────────────────────┼───────────────────┤
│ true │ Doppler recentlogs │ Log Cache │
├──────────────┼────────────────────┼───────────────────┤
│ null │ Doppler streaming │ Log Cache │
├──────────────┼────────────────────┼───────────────────┤
│ false │ Doppler streaming │ Doppler streaming │
└──────────────┴────────────────────┴───────────────────┘

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This PR (code and description) was co-authored by Claude Opus 4 via Claude Code v2.1.87 and carefully reviewed and vetted by its human author.

[jorbaum]

Added a PR to fix the regression: #1352

[jorbaum]

Rebased and made sure the regression still has been fixed.

[jorbaum]

Ran the integration tests with kind-deployment.

I successfully ran the following tests:

• org.cloudfoundry.logcache.v1.*Test (only LogCacheTest.readCounter and LogCacheTest.readEvent failing on kind-deployment, unrelated to my changes)
• org.cloudfoundry.client.v3.*Test (only TasksTest, StacksTest, ProcessesTest, DeploymentsTest failing on kind-deployment, unrelated to my changes)
• org.cloudfoundry.networking.v1.*Test