Larch v6

[jpn--]

This pull request includes updates to documentation links and dependency specifications. The most important changes involve updating outdated URLs for the numba library in the documentation and modifying the version specification for the larch dependency in environment configuration files.

Documentation updates:

• Updated numba URLs in docs/_config.yml and docs/index.md to use the new canonical documentation link (https://numba.readthedocs.io/) instead of the outdated link (https://numba.pydata.org/). [1] [2]

Dependency updates:

• Updated the larch dependency version specification in envs/development.yml and envs/testing.yml to require version 6 or higher (larch>=6). [1] [2]