compile: New implementation of multi-file compilation using mpy-tool.

Add a new implementation of `compile_multi_file()` that uses `mpy-tool`
to find imports. This will work better than the previous implementation
that used Python's `ModuleFinder`, which had several shortcomings.

This is only implemented for MPY ABI v6 for now. To make it work for
older ABIs, we would need to get an older copy of `mpy-tool`, and
backport the json output feature to it.

Author: dlech

CHANGELOG.md

@@ -6,6 +6,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- Changed `pybricksdev.compile.compile_multi_file()` to use `mpy-tool` to find imports
+  instead of Python's `ModuleFinder`.
+
+### Fixed
+- Fixed compiling multi-file projects with implicit namespace packages.
+
 ## [2.3.0] - 2025-10-31
 
 ### Added