* Fix: SIGFPE when drawing grid

Refactor: selection of grid line angles
Co-authored-by: Dalton Luce <[email protected]>

* style: run format

---------

Co-authored-by: Dalton Luce <[email protected]>
Co-authored-by: Dalton Luce <[email protected]>

It is generally discouraged to use nix-env to install packages:
"""
Warning: Using nix-env permanently modifies a local profile of installed packages. This must be updated and maintained by the user in the same way as with a traditional package manager, foregoing many of the benefits that make Nix uniquely powerful. Using nix-shell or a NixOS configuration is recommended instead. 
"""
See for example 
https://search.nixos.org/packages?channel=25.05&show=astroterm&from=0&size=50&sort=relevance&type=packages&query=astroterm

* Add "split_lines" function to split a buffer into an array of lines

- Implement "split_lines" to split a given buffer into an array of
  lines, writing the number of lines to an output pointer.
- Add to src/meson.build

This is helpful for a later commit where `split_lines` will be used to
iterate over the lines in the embedded cities data.

* Refactor "city.c" and add `iter_cities` function.

- The logic in `get_city` for iterating over lines has been moved
  into `split_lines`.
- Refactor "city.c" to use `split_lines`.
- Implement `iter_cities` to apply a callback to all cities.

* Move argument definitions into header file and define with macros.

- Arguments are defined in the new file "arg_definitions.h" and used by
  including this file with appropriate macro definitions.
- Add a "-b|--bash-completions" option which prints bash completions to
  stdout. Use `eval $(astroterm -b)` to enable them in bash.

Explanation: I could have copy-pasted the arguments into the bash
completions code, but this would have made it more brittle to add/change
arguments in the future. This approach means you have a single place
where arguments are defined, and they can be re-used with macros. This
approach of iterating over cities also means that if the list of cities
changes in the future, the completions will remain up-to-date.

* Fix a city with comma-separated name - wasn't getting parsed correctly

* style: run format

* ci: update clang-format

* fix: brute force clang

* fix: update weird city stuff

* fix: update city find search

* fix: fix leak

* test: add tests for iter_city

* fix: fix leak in iter city

* test: add test for split_lines

* style: update test comments

---------

Co-authored-by: Dalton Luce <[email protected]>