This PR changes the `schema` command for viewing the schema of a SQLite
database file. It removes 1 level of nesting (intended to handle
multiple databases in the same connection) that I believe is
unnecessary.
### Before
### After
## Rationale
A SQLite database connection can technically be associated with multiple
non-temporary databases using [the ATTACH DATABASE
command](https://www.sqlite.org/lang_attach.html). But it's not possible
to do that _in the context of Nushell_, and so I believe that there is
no benefit to displaying the schema as if there could be multiple
databases.
I initially raised this concern back in April, but we decided to keep
the database nesting because at the time we were still looking into more
generalized database functionality (i.e. not just SQLite). I believe
that rationale no longer applies.
Also, the existing code would not have worked correctly even if a
connection had multiple databases; for every database, it was looking up
tables without filtering them by database:
6295b20545/crates/nu-command/src/database/values/sqlite.rs (L104-L118)
## Future Work
I'd like to add information on views+triggers to the `schema` output.
I'm also working on making it possible to `ctrl+c` reading from a
database (which is turning into a massive yak shave).
* Test commands for proper names and search terms
Assert that the `Command.name()` is equal to `Signature.name`
Check that search terms are not just substrings of the command name as
they would not help finding the command.
* Clean up search terms
Remove redundant terms that just replicate the command name.
Try to eliminate substring between search terms, clean up where
necessary.
