fix: move dev-only deps to devDependencies and make customPayload opt…

[davidtruong]

…ional

Move copy-webpack-plugin and axios-mock-adapter from dependencies to devDependencies since they are only used in webpack dev config and test files respectively. This prevents consumers from installing unnecessary packages, including the vulnerable serialize-javascript transitive dep.

Also make InAppMessage.customPayload optional to match runtime behavior where the API may return undefined when no custom payload is configured.

Fixes #528, Fixes #538

https://claude.ai/code/session_011XYfVrCRu4H8y24ZEpoboX

JIRA Ticket(s) if any

• MOB-XXXX

Description

Test Steps

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.45%. Comparing base (190a168) to head (54aaad3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #563   +/-   ##
=======================================
  Coverage   74.45%   74.45%           
=======================================
  Files          57       57           
  Lines        2736     2736           
  Branches      798      815   +17     
=======================================
  Hits         2037     2037           
+ Misses        698      658   -40     
- Partials        1       41   +40     

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[davidtruong]

Things are fixed