CI Enhancement: Migrate to container-based runner with Rust caching

[AlexCannonball]

Description

As discussed in #114 (comment), we are currently using devcontainers/ci which ensures maximum environment consistency but lacks Cargo dependency caching. This leads to rebuilding all crates from scratch on every run.

While Option A (current fad97eb) is fine for now, we should consider migrating to Option B if CI times significantly increase.

Proposed Changes (Option B)

1. Switch the Build and Test job from devcontainers/ci to a standard container: runner using our GHCR image.
2. Integrate Swatinem/rust-cache@v2 to cache the target/ directory and Cargo registry.

Pros

• Reduction in CI runtime.
• Faster feedback loop for Pull Requests.

Cons

• Requires the Dev Container image to be pre-published in GHCR to work.
• Slight risk of environment drift if the Dockerfile is changed without updating the image.

Note: This is a "Note Bene" issue to be implemented when build times exceed a reasonable threshold.

[AlexCannonball]

The release workflow may benefit from Swatinem/rust-cache@v2 as well. Please see #133 (comment)