Simple upgrades to Bzlmod migration tool

[kotlaja]

• Fix regex so module name is the same as the workspace name
• Add note to users to add python.toolchain() call for each version in python_register_multi_toolchains. This is hard to select from the migration tool itself due to being visible only for "python_3_x_toolchains" targets in resolved_deps (these targets are not used directly in most of the cases).

[gemini-code-assist]

Code Review

This pull request introduces a couple of useful improvements to the Bzlmod migration tool. The regex for parsing the workspace name is now more robust, and an important note has been added for users of python_register_multi_toolchains. I've suggested a small improvement to the formatting of the new message to ensure it's displayed correctly to the user. The removal of the add_python_repo function is also noted, presumably as dead code removal.

Require module maintainers' approval for newly pushed changes.

[kotlaja]

Fixed it with minor changes so it's more readable to users. With the current change invoking migration tool in the python extension test env looks:

bazel 7.6.1

Detected original workspace name: py_extension

Generating ./resolved_deps.py file - It might take a while...

RESOLVED: `rules_python` has been introduced as a Bazel module.
IMPORTANT: 3.11 is used as a default python version.
                If you need a different version, please change it manually and then rerun the migration tool.
                If you're using `python_register_multi_toolchains`, add `python.toolchain` for each python version.
RESOLVED: `my_deps_2` has been introduced as python extension, with python_version=3.11.
RESOLVED: `my_deps_1` has been introduced as python extension, with python_version=3.11.

Congratulations! All external repositories needed for building `//...` are available with Bzlmod!
IMPORTANT: Fix potential build time issues by running the following command:
        `bazel build --enable_bzlmod --noenable_workspace //...`

IMPORTANT: For details about the migration process, check `migration_info.md` file.

Before this change it was one more IMPORTANT note which was confusing since every next (2+) dep would print:

IMPORTANT: Using existing default python version {python_version} from MODULE.bazel.

which is unsuitable next to the previous IMPORTANT note regarding python version.

[meteorcloudy]

Please address the format issue.

Require module maintainers' approval for newly pushed changes.

[kotlaja]

@meteorcloudy PTAL :)