Feat: save db space by storing horizon as ints

[nhoening]

Description

The belief_horizon DB column uses PostgreSQL Interval (16 bytes). Storing seconds as Integer (4 bytes) saves ~12 bytes per row — up to roughly a fifth of total data size.

SeitaBV/timely-beliefs#231 makes the change in the db model, this PR does the FlexMeasures side

• DB migration from timely-beliefs
• adaptations in logic (very few)
• adapt alembic.ini, so we see errors actually in the CLI
• adapt FM requirements with new timely-beliefs version (only then all tests will pass)
• Added changelog item in documentation/changelog.rst

[read-the-docs-community]

Documentation build overview

📚 flexmeasures | 🛠️ Build #33555584 | 📁 Comparing 543a1a4 against latest (0409655)

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30 files changed · ± 29 modified · - 1 deleted

± Modified

• changelog.html
• configuration.html
• genindex.html
• getting-started.html
• http-routingtable.html
• index.html
• _autosummary/flexmeasures.api.v3_0.accounts.html
• _autosummary/flexmeasures.api.v3_0.jobs.html
• _autosummary/flexmeasures.auth.policy.html
• _autosummary/flexmeasures.data.models.forecasting.pipelines.predict.html
• and 19 more...

- Deleted

• host/multi-tenancy.html

[Flix6x]

Good to note: this PR also effectively changes the minimum/maximum belief horizon from what to what?

[nhoening]

Good to note: this PR also effectively changes the minimum/maximum belief horizon from what to what?

To 68 years.

I'm not sure what was possible with 2 or 3 bytes more (I forgot right now how many we save), but it doesn't seem so important. Probably a millenia or even more than that?