Implement negative temperature conversion (#44)

[Lionheart-Y2J]

What is it?

• [ ] Bugfix
• [x] Feature
• [ ] Codebase improvement

Description of the changes in your PR

• Added +/- button for temperature converter
• Implemented toggleNegative() method in ConverterView to handle sign changes
• Set conditional button visibility (only for temperature)

Before/After Screenshots/Screen Record

• Before: No button for negative values

• After: +/- button appears below numpad (only in temperature converter)

Fixes the following issue(s)

• Fixes #44 (Add +/- to Temperature Unit Converter)

Relies on the following changes

• Updated view_unit_converter.xml layout (new LinearLayout container with id plus_minus_layout)
• Updated UnitConverterActivity.kt button click handler and visibility logic for the +/-
• Updated ConverterView.kt with sign toggle method and numpadClicked

Acknowledgement

• [x] I read the contribution guidelines.

[Aga-C]

I've tested and found two issues:

• +/- button should also work when there's no value. Most people first enter -, then the rest of the number.
• Deleting a negative number causes a crash.

There are also two issues that I'm not sure whether we should address them in this PR:

• There's no such thing as negative Kelvins and negative Rankines. It shouldn't be possible to enter a negative value for these units.
• By analogy, you shouldn't allow entering values for Celsius and Fahrenheit that are below absolute zero.

[Lionheart-Y2J]

I fixed the crash issue (deleting negative value resets to 0) and added the possibility to use the - before entering a number.

Concerning the other remarks, I made sure to enforce temperature limits during input by automatically adjusting values that exceed absolute zero for each unit type: Celsius cannot go below -273.15, Fahrenheit below -459.67, and Kelvin/Rankine are blocked entirely from being negative (minimum 0)

[Lionheart-Y2J]

Hello @Aga-C Just checking in to see if there's anything else needed on this PR. I haven't planned to make any changes unless needed so if everything looks good, a review would be much appreciated. Thanks

[naveensingh]

Hi! @Lionheart-Y2J

I'll do a final review and merge this soon.

Thanks.

[naveensingh]

The functionality itself seems to work. Left some comments and nitpicks regarding the code.