feat!: mount function for injecting aditional files into the workspace

[Power-el-Tanke]

Summary

Introduces the mount abstraction for injecting files into the pipeline workspace. This PR modifies the IR by modifying the Step's schema. The cmd and env fields are removed, instead, the action is introduced and accepts a field of the type StepAction, which is an union of Command (a structure that carries the 2 mentioned removed fields) and Mount (which has the source and destination paths of a mount).

It can be used in 2 ways:

import harmont as hm
# From a Step object
hm.scratch().mount(from_="../path/to/inject", to=path/inside/the/workspace")

# As a plain function
hm.mount(from_="../path/to/inject", to="path/inside/the/workspace")

Both source and destination should be relative to the workspace's path. The destination file/directory should exists unless you set the strictkwarg to False (defaults to True).

Tests

Most of the tests (and only the tests) were modified with the help of an LLM to fit with the new schema. All were human reviewed. An integration test was handwritten in crates/hm/tests/local_e2e.rs for the new feature. There is also the crates/hm-dsl-engine/harmont-py/tests/tests_step_mount.py file for the python side.

Minor changes:

• docker backed is able to inject singular files