fix: Crash in MPSession description

[denischilik]

Background

Fixes a crash that could occur when MPSession properties were accessed concurrently during session persistence. The root cause was thread-unsafe access to session properties when building the description string, combined with a deprecated MPListenerController callback.

What Has Changed

• Made MPSession properties atomic for thread-safe concurrent access
• Removed deprecated MPListenerController callback from session persistence path
• Cached MParticle shared instance in beginSessionWithIsManual to avoid redundant lookups and potential race conditions

Screenshots/Video

N/A

Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have tested this locally.

Reference Issue (For employees only. Ignore if you are an outside contributor)

• Closes https://rokt.atlassian.net/browse/SDKE-1113

[github-actions]

📦 SDK Size Impact Report

Measures how much the SDK adds to an app's size (with-SDK minus without-SDK).

Metric	Target Branch	This PR	Change
App Bundle Impact	1.82 MB	1.82 MB	+N/A
Executable Impact	896 bytes	896 bytes	+N/A
XCFramework Size	9.49 MB	9.48 MB	-4 KB

➡️ SDK size impact change is minimal.

Raw measurements

Target branch (main):

{"baseline_app_size_kb":84,"baseline_executable_size_bytes":75464,"with_sdk_app_size_kb":1944,"with_sdk_executable_size_bytes":76360,"sdk_impact_kb":1860,"sdk_executable_impact_bytes":896,"xcframework_size_kb":9716}

This PR:

{"baseline_app_size_kb":84,"baseline_executable_size_bytes":75464,"with_sdk_app_size_kb":1944,"with_sdk_executable_size_bytes":76360,"sdk_impact_kb":1860,"sdk_executable_impact_bytes":896,"xcframework_size_kb":9712}

[BrandonStalnaker]

LGTM!