Add CI workflow and flake checks

[ProjectInitiative]

This PR adds a CI workflow to the project.
It refactors crane.nix to expose the build configuration, which is then used in flake.nix to define checks for:

• The package build (including tests)
• Clippy linting
• Rust formatting

The CI workflow runs nix flake check to execute these checks. It also includes a necessary AppArmor configuration step for Nix sandboxing on Ubuntu runners.

---

PR created automatically by Jules for task 818934876918795744 started by @ProjectInitiative

[google-labs-jules]

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[ProjectInitiative]

please fix the build error: error: builder for '/nix/store/ky46d7rndy225d49zr6a2n7hm54067a9-loft-fmt-0.2.0.drv' failed with exit code 1;
last 10 log lines:
> Diff in /build/source/src/s3_uploader.rs:159:
> for object in contents {
> if let Some(key) = object.key {
> if key.ends_with(".narinfo") {
> - let processed_key = if let Some(stripped) = key.strip_prefix("sha256:") {
> + let processed_key = if let Some(stripped) = key.strip_prefix("sha256:")
> + {
> stripped.to_string()
> } else {
> key
For full logs, run 'nix log /nix/store/ky46d7rndy225d49zr6a2n7hm54067a9-loft-fmt-0.2.0.drv'.
error: build of '/nix/store/jal8dlsiqysxijxv4rmjhwllb5df7dyl-loft-clippy-0.2.0.drv', '/nix/store/ky46d7rndy225d49zr6a2n7hm54067a9-loft-fmt-0.2.0.drv', '/nix/store/yh6nd3673cm8gy35qm2fqi6pasmrkypi-loft-0.2.0.drv' failed

[google-labs-jules]

please fix the build error: error: builder for '/nix/store/ky46d7rndy225d49zr6a2n7hm54067a9-loft-fmt-0.2.0.drv' failed with exit code 1;
last 10 log lines:
> Diff in /build/source/src/s3_uploader.rs:159:
> for object in contents {
> if let Some(key) = object.key {
> if key.ends_with(".narinfo") {
> - let processed_key = if let Some(stripped) = key.strip_prefix("sha256:") {
> + let processed_key = if let Some(stripped) = key.strip_prefix("sha256:")
> + {
> stripped.to_string()
> } else {
> key
For full logs, run 'nix log /nix/store/ky46d7rndy225d49zr6a2n7hm54067a9-loft-fmt-0.2.0.drv'.
error: build of '/nix/store/jal8dlsiqysxijxv4rmjhwllb5df7dyl-loft-clippy-0.2.0.drv', '/nix/store/ky46d7rndy225d49zr6a2n7hm54067a9-loft-fmt-0.2.0.drv', '/nix/store/yh6nd3673cm8gy35qm2fqi6pasmrkypi-loft-0.2.0.drv' failed

I've fixed the formatting issue in src/s3_uploader.rs to match the expected style.

[ProjectInitiative]

building '/nix/store/z1l4fyy86545yj8ky5vgcfjy90gc9b06-loft-0.2.0.drv'...
building '/nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv'...
error: builder for '/nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv' failed with exit code 101;
last 10 log lines:
> |
> 480 | let _ = sleep(Duration::from_secs(5));
> | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> |
> = help: consider awaiting the future or dropping explicitly with std::mem::drop
> = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_future
>
> error: could not compile loft (lib test) due to 53 previous errors
> warning: build failed, waiting for other jobs to finish...
> error: could not compile loft (lib) due to 53 previous errors
For full logs, run 'nix log /nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv'.
error: build of '/nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv', '/nix/store/z1l4fyy86545yj8ky5vgcfjy90gc9b06-loft-0.2.0.drv' failed

[google-labs-jules]

building '/nix/store/z1l4fyy86545yj8ky5vgcfjy90gc9b06-loft-0.2.0.drv'...
building '/nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv'...
error: builder for '/nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv' failed with exit code 101;
last 10 log lines:
> |
> 480 | let _ = sleep(Duration::from_secs(5));
> | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> |
> = help: consider awaiting the future or dropping explicitly with std::mem::drop
> = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#let_underscore_future
>
> error: could not compile loft (lib test) due to 53 previous errors
> warning: build failed, waiting for other jobs to finish...
> error: could not compile loft (lib) due to 53 previous errors
For full logs, run 'nix log /nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv'.
error: build of '/nix/store/cb5cp500ry7s5yrgsb2hrc0j80kykvcv-loft-clippy-0.2.0.drv', '/nix/store/z1l4fyy86545yj8ky5vgcfjy90gc9b06-loft-0.2.0.drv' failed

I've fixed the clippy::let_underscore_future warnings in src/nix_utils.rs by correctly awaiting the tokio::time::sleep calls.