Cleaning td write

Description

Some small changes to src/td/td_write, to allow for some unsupported k-point parallelization and to forbid some run mode not supported for periodic systems.

News snippet

Adding a k-point parallelization support for TDOutput=td_proj and forbidding TDOutput=populations for solids, as it is not supported.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.