Add Docker-based compiler build system

[carpikes]

This PR introduces a Dockerfile and a helper script that allow building any supported compiler toolchain in a fully reproducible Docker environment. Once Docker completes the build, it automatically packages the resulting toolchain into a tar.gz archive, which is written directly inside the compiler/ directory.

This makes compiler builds reproducible, isolated from the host environment and easy to run with a single command.
The system has been tested only on Linux so far.

Usage example

$ cd miosix/_tools/compiler
$ ./build_with_docker.sh gcc-15.2.0-mp4.0
# Wait until the build completes

$ ls -l *.tar.gz
-rw-r--r-- 1 al al 261922888  9 dic 15:39 arm-miosix-eabi-gcc-15.2.0-mp4.0.tar.gz

What's included

• Dockerfile: defines a multi-stage build that downloads, builds, packages the toolchain and writes the output archive into the current compiler/ directory.
• build_with_docker.sh: helper script that: lets you choose a compiler folder and runs the Docker build