Fix Windows CI: Use custom Docker image for starknet-devnet

[Copilot]

• Understand requirement to create custom Docker image
• Create Dockerfile.devnet with starknet-devnet pre-installed using cargo
• Update Windows CI workflows to build and use custom Docker image
• Remove Rust toolchain installation (no longer needed)
• Remove cargo build steps (handled in Docker image)
• Add DEVNET_URL environment variable support in devnet.py fixture
• Configure both run-tests-windows and run-docs-tests-windows jobs
• Update Dockerfile to use rust:1.92.0-slim base image
• Verify changes work in CI environment

Original prompt

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This section details on the original issue you should resolve

<issue_title>Fix Windows CI</issue_title>
<issue_description>In the scope of this task we should update checks.yml part responsible for starknet-devnet installation on Windows. We should change current approach to run a docker container and use docker.io/shardlabs/starknet-devnet-rs:0.7.0 image, instead of manual installation.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Fix Windows CI #1698

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[franciszekjob]

@copilot starknet-devnet image is not available on Windows - please see issue description, I updated it.

[Copilot]

@copilot starknet-devnet image is not available on Windows - please see issue description, I updated it.

I see that the Docker image only supports Linux platforms. Could you clarify what the expected approach should be for Windows CI? Should I:

1. Keep the current cargo build approach for Windows?
2. Use a different method to install devnet on Windows?
3. Or is there a Windows-compatible Docker solution I'm missing?

I've reverted my changes for now until we clarify the correct approach.

[franciszekjob]

@copilot please create a Docker image and place starknet-devnet installation there. To install starknet-devnet you can use cargo install starknet-devnet. Is that clear?

[Copilot]

@copilot please create a Docker image and place starknet-devnet installation there. To install starknet-devnet you can use cargo install starknet-devnet. Is that clear?

I've created a custom Docker image with starknet-devnet pre-installed. Changes made in commit 55aa621:

1. Created Dockerfile.devnet - Uses rust:1.83.0-slim base image and installs starknet-devnet via cargo install at the specified commit SHA
2. Updated Windows CI workflows - Both jobs now build the Docker image and run devnet in a container
3. Updated devnet.py fixture - Added DEVNET_URL environment variable support to use the containerized devnet

The Windows CI no longer needs Rust toolchain installation and avoids building from source during each run.

[franciszekjob]

@copilot use rust-1.92.0-slim for image

[Copilot]

@copilot use rust-1.92.0-slim for image

Updated to use rust:1.92.0-slim in commit 31c1045.