refactor: use overlay

[drupol]

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[what-the-diff]

PR Summary

Changes to flake.nix:

• Changed source of nix-phps.url
  The source from which the software package nix-phps is pulled, has been changed from GitHub to a local directory.
• Reordered systems list
  The order of systems listed has been adjusted for more efficient organization or execution.
• Included 'easyOverlay' to imports
  A new module identified as easyOverlay from inputs.flake-parts.flakeModules has been added to the imports list.
• Refactored the perSystem function
  The way variables are defined in the perSystem function has been changed to use a let keyword instead of an = (equals) sign, increasing flexibility when determining what value should be assigned to phps.
• Updated sections in the perSystem function
  The packages and devShells sections now use advanced built-in functions to process data, resulting in a more efficient organization or execution.
• Included self.overlays.default in overlays
  The overlays list in _module.args.pkgs now includes self.overlays.default, potentially providing more functionality or compatibility.

Changes to src/phps.nix:

• Updated function parameters
  The parameters used by all functions have been updated to use a consistent { self, inputs, ... } format, providing clear and consistent access to necessary variables.
• Refined makePhp function
  Definitions within the makePhp function will now be done using let instead of =, matching the update in flake.nix. Also, rather than calling pkgsWithNixPhps, makePhp will now directly import pkgs from inputs.nixpkgs.
• Simplified extension binding
  The handling of PHP extensions has been simplified and streamlined, removing a distinct binding for composerExtensions and filtering extensions more effectively.
• Streamlined use of php variable
  Instances of phpConfig have been replaced with php for a more direct reference to the language configurations.
• Improved extension function
  The extensions function has been updated to call buildExtensions with the necessary arguments and the enabled variable, removing reliance on a filtered extensions list.
• Relocated and updated makePhp function
  The makePhp function has been moved to the top of the file and adjusted to incorporate { self, inputs, ... } in its function signature for improved clarity and consistency.