Prepare 0.18.0 release

[mtreinish]

This commit makes a few updates to the repository to prepare for the release of rustworkx 0.18.0. First it updates the version numbers to 0.18.0. It then reorganizes the release notes by moving the 0.18.0 note files into a separate directory, and updating them for syntax issues and clarity. A prelude release note is added to highlight the features of the release. As part of this a new subsection mechanism is added to the release notes to have a subsection for rustworkx-core features and upgrade notes.

Finally, some small documentation fixes are made to reflect the current state of the project with this release. Mainly removing indirect references to support for Python versions older than 3.10, incorrectly documenting the EoL of the retworkx name as the pending 1.0 release, and stale instructions to manually install setuptools-rust if pip or your PEP-517 compliant builder doesn't.

This is on hold until the remaining 0.18 PRs merge. The current list of open PRs is:

• Bump rand crates to 0.10.x releases #1604
• Add longest_path_length to rustworkx_core::dag_algo #1605
• Bump ndarray from 0.16.1 to 0.17.2 #1599 (needs to be rebased now that Relax ndarray version for rustworkx-core #1602 has merged)

Closes: #1529

[IvanIsCoding]

I will send a PR today to publish a 3.14t wheel. At least for Linux and macOS. Right now, there is a skip we will simply remove the skip.