refactor: update persistence module to TS

[jaissica12]

Background

• Continuing the effort to migrate remaining JavaScript modules to TypeScript for improved type safety and developer experience across the SDK codebase.

What Has Changed

• Converted src/persistence.js to src/persistence.ts with full type annotations on all methods, parameters, and return types
• Updated src/persistence.interfaces.ts with corrected and expanded interface definitions to support the conversion
• Updated test/jest/persistence.spec.ts with type adjustments for the converted module

Screenshots/Video

• Tested on rokt-web-playground

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.

Additional Notes

• var declarations replaced with const/let (SonarCloud compliance)
• toGMTString() replaced with toUTCString() (functionally equivalent, toGMTString is deprecated)
• JSON.stringify(..., 0, 2) replaced with JSON.stringify(..., null, 2) (functionally equivalent, satisfies TS type checker)

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

• Closes https://go/j/SDKE-1107

[sonarqubecloud]

Quality Gate passed

Issues
41 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cursor]

PR Summary

Medium Risk
Touches cookie/localStorage and MPID persistence used across identity and sync; changes are typing-focused but any subtle decode/encode or null-handling mismatch could affect stored user state.

Overview
Migrates the persistence layer from JavaScript to TypeScript: persistence.js becomes persistence.ts, with the constructor and all cookie/localStorage methods typed against IPersistence / IPersistenceMinified.

persistence.interfaces.ts is tightened to match runtime behavior: nullable getPersistence, numeric first/last seen times, optional MPID/time args, encodePersistence taking a JSON string, decodePersistence returning string | null, and getDomain using Document.

Implementation edits are mostly typing and style: var → const/let, closure self → this, Dictionary casts where store/helpers are not fully typed, and toGMTString() → toUTCString() for cookie expiry. Jest persistence tests now hold an IPersistence instance instead of the untyped class.

^{Reviewed by Cursor Bugbot for commit 4928096. Bugbot is set up for automated code reviews on this repo. Configure here.}