fix(build): double relative manifest path

[remimimimimi]

Problem description

When --manifest-path is specified for pixi build it gets double prefixed and fails with error like this:

remi@mi:~/Projects/Mine/pixi/main$ pixi build --manifest-path examples/pixi-build/array-api-extra/pixi.toml
Error:   × failed to discover a valid project manifest, the source path '/home/remi/Projects/Mine/pixi/main/examples/pixi-build/array-api-extra/examples/pixi-build/array-api-
  │ extra/pixi.toml' could not be found

Which happens because given manifest path is added to the discovered workspace root directory.

Solution

Compute relative path from workspace root to the given (canonicalized) manifest path.

Testing

Run following command from the root dir of the repository to test that it doesn't work on main:

pixi build --manifest-path examples/pixi-build/array-api-extra/pixi.toml

and run

cargo r -- build --manifest-path examples/pixi-build/array-api-extra/pixi.toml

to see that it works with this fix.

Notes

I'm still not quite sure that this fix is a correct way to do it, since we have more logic in the resolve_typed_path, so feedback is appreciated!