pybricksdev/compile: use relative paths

In `compile_multi_file()` modules other than the main one were not
using relative paths. This worked but resulted in the full path being
compiled into the the resulting .mpy file which takes up more space.

This change makes sure that all modules are compiled with relative paths
instead.

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- Use relative paths when compiling multi-file projects.
+
 ## [1.0.0-alpha.48] - 2024-05-04
 
 ### Changed

pybricksdev/compile.py

@@ -129,7 +129,10 @@ async def compile_multi_file(path: str, abi: Union[int, Tuple[int, int]]):
     for name, module in finder.modules.items():
         if not module.__file__:
             continue
-        mpy = await compile_file(module.__file__, abi_major)
+
+        relative_file = os.path.relpath(module.__file__, os.path.dirname(path))
+
+        mpy = await compile_file(relative_file, abi_major)
 
         parts.append(len(mpy).to_bytes(4, "little"))
         parts.append(name.encode() + b"\x00")