fix(ui-kit): preserve falsy initial and state values

[Shreyas2004wagh]

Acceptance Criteria fulfillment

• Preserve valid falsy initial values such as 0 and '' in UI Kit value resolution
• Preserve valid falsy state values from UiKitContext instead of incorrectly falling back to initial values
• Add regression tests covering falsy initial values and falsy context state values

Fixes #1235

Video/Screenshots

N/A

PR Test Details

• Added regression tests for getInitialValue
  • preserves empty string initial values
  • preserves zero-valued initial values
  • preserves empty string option values
• Added regression tests for useUiKitState
  • preserves zero values from context state
  • preserves empty string values from context state
• Targeted test result: 2 suites passed, 5 tests passed
• File-scoped lint passed for:
  • packages/ui-kit/src/utils/getInitialValue.js
  • packages/ui-kit/src/hooks/useUiKitState.js