Expose Start/Stop API to Objc

[mariedm]

What and why?

The startRecording and stopRecording public APIs were introduced in #1986 to allow manual control over session recording. However, these APIs were not exposed to Objective-C, limiting access for ObjC users. This PR addresses that gap.

How?

This PR adds startRecording and stopRecording methods to the DDSessionReplay class, making them accessible from Objective-C.

Review checklist

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration)
• [ ] Make sure each commit and the PR mention the Issue number or JIRA reference
• [ ] Add CHANGELOG entry for user facing changes

[datadog-datadog-prod-us1[bot]]

Datadog Report

Branch report: mariedm/add-start-stop-objc-apis Commit report: 154505a Test service: dd-sdk-ios

:white_check_mark: 0 Failed, 3471 Passed, 0 Skipped, 2m 21.86s Total Time :small_red_triangle_down: Test Sessions change in coverage: 3 decreased, 4 increased, 7 no change

:small_red_triangle_down: Code Coverage Decreases vs Default Branch (3)

• test DatadogCoreTests tvOS 78.5% (-0.19%) - Details
• test DatadogTraceTests iOS 54.17% (-0.09%) - Details
• test DatadogCrashReportingTests tvOS 26.8% (-0.02%) - Details