feat(nix) :: add a development shell

[81reap]

Adds an optional dev shell with all of the tools needed to build SQLPage at the same versions the CI uses.

If you have nix installed or use NixOS you can now run ::
(1) nix develop :: assumes the dev shell
(2) nix fmt :: runs rustfmt, biome, and nixfmt
(3) nix run .#test-rust
(4) nix run .#test-browser
(5) nix run .#test-examples
(6) nix flake check

[81reap]

@lovasoa I suspect #1491 got closed due to stack issues. would appreciate to hear your thoughts if i misread the situation

[81reap]

This requires #1487 to be merged first. this was ran on MacOS

$ nix flake check
error:
       … while checking flake output 'apps'
         at /nix/store/ysjjcfyfmps6n74jdkk7p00swvgw610l-source/flake.nix:205:7:
          204|
          205|       apps = forEachSystem (
             |       ^
          206|         pkgs:

       … while checking the app definition 'apps.aarch64-darwin.lint-rust'

       … while calling the 'getAttr' builtin
         at <nix/derivation-internal.nix>:50:17:
           49|     value = commonAttrs // {
           50|       outPath = builtins.getAttr outputName strict;
             |                 ^
           51|       drvPath = strict.drvPath;

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: opening file '/nix/store/ysjjcfyfmps6n74jdkk7p00swvgw610l-source/rust-toolchain.toml': No such file or directory