feat: Add time selection to date picker with ISO datetime storage

[vijay2909]

Requirement
The issue required adding time selection capability to the existing date picker functionality. Previously, users could only select dates without specific times, which limited precision for time-sensitive features.

Changes Made

1. Enhanced Picker Flow:

• Modified date selection to trigger time picker automatically after date is chosen
• Combined date and time into a single ZonedDateTime object
• Updated UI to display both date and time in the input field

2. Data Storage Migration:

• Changed database storage format from milliseconds (long) to ISO 8601 strings
• ISO format provides timezone awareness and better interoperability
• Maintained backward compatibility through migration handling

3. DateTimeUtils Class:

• Created utility class with helper methods for datetime conversions
• Added methods for formatting, parsing, and validation
• Implemented comprehensive test coverage with 100% pass rate

4. Testing:

• Added complete test suite for DateTimeUtils using Espresso and Robolectric
• Verified date-time combination logic and formatting
• Ensured edge cases and timezone handling work correctly

Technical Details

• Uses MaterialDatePicker and MaterialTimePicker for consistent UI
• ZonedDateTime for proper timezone handling throughout the application
• ISO 8601 format for future-proof data storage and exchange

Maintains existing API contracts while extending functionality

The implementation provides users with precise datetime selection while maintaining data integrity and test reliability.

Fixes: #2284

[TheLastProject]

Wow, that was fast :)

The description sounds like this is going in the right direction. Thank you for this.

I might take a while until I can review this, I want to try to finish up #2716 somewhat soon to fix issues with barcodes with Cyrillic and similar issues, and I have a busy week coming up, but after that I'll definitely take a look at this :)