SDK-1400 Improve Java DX

[jhaven-stytch]

Linear Ticket: SDK-1400

Changes:

1. Adds @JvmStatic annotation to object properties (to prevent having to type StytchClient.INSTANCE.[property])
2. Adds @JvmOverloads constructors to data classes, where applicable
3. Changes our usage of UInt to simple Int (because Java doesn't have UInt, and UInt prevents usage of @JvmOverloads; also, we were casting it to Int before making the request anyway, so this reduces unnecessary overhead)
4. Adds manual overloads for configure methods (ran into some oddities with @JvmOverloads on these methods)
5. Made all top-level client properties val instead of vars with internal set, because it was causing the non-accessible setters to be visible; These were only set as var for unit tests, and I removed those few tests that relied on that.
6. Adds a barebones Java example app (using StytchUI) for testing the above changes
7. Ensure versions of libs/plugins are in sync between projects (need to move to version catalogs in a future ticket)
8. Some general automated cleanup/linting from running Inspection tool

Notes:

Checklist:

• I have verified that this change works in the relevant demo app, or N/A
• I have added or updated any tests relevant to this change, or N/A
• I have updated any relevant README files for this change, or N/A