Why in the world would you want to develop something that doesn’t follow the coding rules required by your org, just so you can go back and fix everything before submitting a PR? That’s just extra work.
Because you want to know if the first half of the code works at all before you write the whole second half.
Finding all the bits that will be used by the second half and changing the declarations to just expressions is a bunch of extra work. As is adding placeholder code to use the declared variables.
I’m having a hard time envisioning a situation where testing my code requires a bunch of unused variables. Just don’t declare the variables until you’ve started writing the code that uses them…
Most of the time you don’t write the code, you change it.
I had tons of situations where I wanted to test deleting a code block which just happened to use an imported library, which the compiler is now complaining about because it’s no longer being used.