Simplify the Makefile by removing unnecessary variables and commands. This improves readability and maintainability of the Makefile.

- Removed the `MAMBA` variable and replaced all occurrences with `micromamba --yes --name=$(NAME)`
- Removed the `RUN` variable and replaced all occurrences with `poetry run`
- Removed the `POETRY` variable and replaced all occurrences with `poetry`

These changes make the Makefile easier to understand and modify in the future.