feat: Add nix/flake support

[chives101]

This PR is a counter part of mimblewimble/grin#3743 , which adds nix/flake support to the daemon. The following description is almost identical.

Motivation

This PR enables power users to easily and reliably build the project from source code.

Expectation

A user with the nix package manager installed can build the project with the following command:

nix build github:mimblewimble/grin-wallet

and expect the resulting binaries in ./result/bin/.

Testing

If flake hasn't been enabled, use nix build --extra-experimental-features 'nix-command flakes' in place of nix build.

A test run for this PR can be achieved using my forked repo with the following command:

nix build github:chives101/grin-wallet/flake and expect a binary at ./result/bin/grin-wallet.

Or by entering the project folder and do nix build after applying the PR.

Dev notes

This PR is the result of a simple adaptation of the code from this blog post:

https://www.tweag.io/blog/2022-09-22-rust-nix/

[syntaxjak]

✅ Testing Summary

Tested with the following steps:

git clone https://github.com/mimblewimble/grin-wallet.git
cd grin-wallet

git remote add chives101 https://github.com/chives101/grin-wallet.git
git fetch chives101 flake
git checkout -b test-flake chives101/flake

nix build --extra-experimental-features 'nix-command flakes'
./result/bin/grin-wallet init

Result:
The project built successfully without any errors. I expected potential issues such as outdated cargo hashes or overlay scope problems, but neither occurred.

The build completed cleanly, and the resulting grin-wallet binary initialized as expected. The only remaining step would be to confirm functionality via live transactions, but I see no reason this would fail.

Conclusion:
This PR appears fully functional and ready to be merged into the main branch. Excellent work bringing proper flake support to grin-wallet!

[Anynomouss]

Update version = "5.3.0"; to whatever the latest version is 5.4.0-alpha.1.
Update nixpkgs.url = "github:NixOS/nixpkgs/release-23.11"; to nixpkgs.url = "github:NixOS/nixpkgs/release-25.05";

[chives101]

Update version = "5.3.0"; to whatever the latest version is 5.4.0-alpha.1. Update nixpkgs.url = "github:NixOS/nixpkgs/release-23.11"; to nixpkgs.url = "github:NixOS/nixpkgs/release-25.05";

Updated.