Using the view `information_schema.columns` is slow compared to a simplified query using PG catalog tables. Here we propose to cherry pick the parts of the view that we actually use.

Below we show the timings of both queries as reported by the system on an upgrade 18->master with a runbot DB (many modules installed). All values are in milliseconds.
```
Original:
    min: 0.931
    max: 16.786
    mean: 1.8790601284296555
    sum: 25750.64
    len: 13704
New:
    min: 0.224
    max: 11.832
    mean: 0.8649024372446001
    sum: 11852.623
    len: 13704
```
Total time spent in queries was halved as seen in the `sum` statistic above.

Technically, the new queries are base on the original information schema view definition as returned by `\d+ information_schema.columns`. With all unused info removed.

Description of the issue/feature this PR addresses:

Current behavior before PR:

Desired behavior after PR is merged:




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Forward-Port-Of: odoo/odoo#285419
Forward-Port-Of: odoo/odoo#216309

`TestForumInternals` assumed that only the base forum and the forum created by the test setup existed in the database.

This is not true when tests are run with demo data. In particular, `website_slides_forum` creates additional demo forums, causing `test_assert_initial_values` and the forum count assertions to fail even though the forum behavior itself is correct.

This commit avoids relying on the global number of existing forums and instead scope the initial-value assertions to the forums owned by the test itself.

For forum count tests, we use the count observed at the beginning of the test as a baseline and assert the expected deltas after creating or updating forums. This keeps the test focused on the behavior being tested while allowing unrelated forums to already exist.

This also avoids modifying, archiving, or explicitly filtering demo records, and does not introduce a dependency on modules such as `website_slides_forum`.

The tests therefore behave identically on databases both with and without demo data.

[error-241100
](https://runbot.odoo.com/odoo/error/241100)


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