feat: Enhance local launcher logic with user threshold check

[guillermot]

Summary

Enhance local launcher logic with user threshold check. This commit implements a 50/50 traffic split mechanism for the Rokt Local Launcher feature by adding a user threshold check.

Changes Made

Enhanced Local Launcher Logic (src/Rokt-Kit.js):

• Added _isUserAboveLocalLauncherThreshold() function that implements a 50% threshold check using Math.random() > 0.5
• Modified isPartnerInLocalLauncherTestGroup() to include the threshold check alongside the existing isLocalLauncherEnabled configuration
• Users are now randomly assigned to either local or remote launcher based on the threshold

Comprehensive Test Coverage (test/src/tests.js):

• Added test case for users below threshold (random = 0) → should create remote launcher
• Added test case for users above threshold (random = 1) → should create local launcher
• Added Math.random mock setup to ensure deterministic test behavior

Impact:

Enables gradual rollout of the local launcher feature with 50/50 traffic split
Maintains backward compatibility with existing configuration
Provides robust test coverage for the new threshold logic

Testing Plan

{explain how this has been tested, and what additional testing should be done}