Tag beta version for Cantera 3.1.0

[speth]

Changes proposed in this pull request

• Draft release notes for Cantera 3.1.0
• Bump version to 3.1.0b1 (this should be the tagged commit)

This should be merged after #1808.

Checklist

• [x] The pull request includes a clear description of this code change
• [x] Commit messages have short titles and reference relevant issues
• [x] Build passes (scons build & scons test) and unit tests address code coverage
• [x] Style & formatting of contributed code follows contributing guidelines
• [x] The pull request is ready for review

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.26%. Comparing base (e36c9b9) to head (35849bc). Report is 9 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1810 +/- ## ======================================= Coverage 73.26% 73.26% ======================================= Files 383 383 Lines 54620 54620 Branches 9099 9099 ======================================= Hits 40016 40016 Misses 11601 11601 Partials 3003 3003 ```

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[speth]

Hopefully and yes, respectively. I don't think there's a need to hold the beta for either of these.