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

[81reap]

it works. tested on MacOS to make sure its not just working on my NixOS machine

> nix flake check
warning: The check omitted these incompatible systems: aarch64-linux, x86_64-linux
Use '--all-systems' to check all.

> cargo          
zsh: command not found: cargo

> nix develop

$ cargo
Rust's package manager
...

$ nix fmt
traversed 1118 files
emitted 169 files for processing
formatted 169 files (0 changed) in 699ms

tests pass as well, but output is too long to post in this comment