fix: move torch forward to 2.3.1 (#622)
After some good testing by Marc, we can see that the audio quality is
comparable with 2.3 and 2.1.
Torch 2.1.0 has vulnerabilities and is no longer available in some
environments, so we decided to bump to 2.3.1.
At the EV dev meeting, we decided not to move to 2.4 yet as there is a Future
Proofing warning we need to handle first (see #621).
Replaces #521, done in pyproject.toml instead of requirements.txt.
Fixes https://github.com/EveryVoiceTTS/EveryVoice/security/dependabot/2
Fixes https://github.com/EveryVoiceTTS/EveryVoice/security/dependabot/4
Fixes https://github.com/EveryVoiceTTS/EveryVoice/security/dependabot/10
Fixes https://github.com/EveryVoiceTTS/EveryVoice/security/dependabot/11
Fixes #558
