fix(webpack): prevent state race on multiple script injections

[dev-robin-hood]

Closes #3222

Added a global lock in window.__WPP_INIT_LOCK__ that tracks initialization state across script re-executions. The lock has three states: not_started, initializing, and completed.

When injectLoader() runs, it checks this global state. If init already finished, it syncs local variables from global state and returns. If init is currently running, it waits for the stored Promise to complete then syncs state. Only starts a new init if nothing has run yet.

Refactored the initialization code into separate functions (performMetaLoaderInit, performWebpackLoaderInit, performInitialization) and made sure state updates go to both local variables and the global lock. Timer IDs are tracked globally so we can clean them up instead of leaving orphaned timers from previous script executions.

This stops multiple instances from racing with conflicting timers and state. Works whether you re-inject before, during, or after init completes. No changes to the public API.

[manfe]

How did you test the race condition? To simulate it?

[dev-robin-hood]

How did you test the race condition? To simulate it?

I ran two built scripts at the same time; if you want, I can create two Chrome extensions, each with a different console log and using the global WPP.