refactor: extract KeyboardStateManager from GeneralKeyboardIME (#426)

[prince-0408]

Description

This PR is Part 7 in modularizing GeneralKeyboardIME for #426.

It extracts ScribeState tracking, state transitions, invalid command state recording, and state query helpers out of GeneralKeyboardIME.kt into a standalone, unit-testable helper class KeyboardStateManager.

Detailed Changes Table:

File / Component	Changes Applied	Detailed Impact
KeyboardStateManager.kt	Created standalone helper encapsulating currentState (ScribeState), invalidCommandSource (ScribeState), transition methods (moveToState, moveToIdle, setInvalidState, reset), and state query getters (isIdle, isSelectCommand, isCommandBarActive, isInvalid, isAlreadyPlural).	Extracts state management responsibility out of GeneralKeyboardIME.kt into a dedicated, unit-testable class.
GeneralKeyboardIME.kt	Instantiated stateManager and delegated currentState & invalidCommandSource properties. Refactored state transition methods (moveToIdleState(), onScribeKeyOptionsClicked(), onTranslateClicked(), onConjugateClicked(), onPluralClicked(), handlePluralOrTranslateState(), handleConjugateState()) to delegate to KeyboardStateManager.	Reduces complexity and responsibility of GeneralKeyboardIME.kt while preserving 100% backward compatibility for external callers.
KeyboardStateManagerTest.kt	Added unit tests covering initial state defaults, state transitions (moveToState, moveToIdle), invalid state source recording (setInvalidState), query getters (isIdle, isCommandBarActive, etc.), and state reset (reset).	Ensures 100% unit test coverage for state management logic.

Key Benefits:

• Modular & Decoupled Architecture: Moves state management logic out of GeneralKeyboardIME.kt into a single-responsibility helper class.
• Improved Testability: State transitions can now be unit-tested independently of Android service lifecycles.
• Zero Behavioral / API Breakage: Preserves exact state transitions and retains property delegation for zero breaking changes across existing helpers (KeyHandler, BackspaceHandler, SuggestionHandler, ClipboardHandler, KeyboardUIManager, etc.).

Related Issue

Refactors part of #426

[andrewtavis]

Thanks for the PR, @prince-0408! Maintainers are a bit busy for the next few days. @linreal, would you have a moment to take a look again? 😊

[linreal]

lgtm!

[andrewtavis]

praise: All's looking good on my end as well in terms of code and functionality. Thanks, @prince-0408! And thanks for the initial review, @linreal!

[prince-0408]

praise: All's looking good on my end as well in terms of code and functionality. Thanks, @prince-0408! And thanks for the initial review, @linreal!

Hi @andrewtavis There are a few more refactoring PRs that I think would be good to raise. If you’re okay with it, I can work on those as well and create the PRs.

[andrewtavis]

Sounds good, @prince-0408! Feel free to write into #426 with your ideas, if they're not already covered by what's been planned there already.