Allow unsetting config values similar to `git config unset`.
```bash
$ jj config set --user some-key some-val
$ jj config get some-key
some-val
$ jj config unset --user some-key
$ jj config get some-key
Config error: configuration property "some-key" not found
For help, see https://martinvonz.github.io/jj/latest/config/.
```
Unsetting a key, which is part of a table, might leave that table empty.
For now we do not delete such empty tables, as there may be cases where
an empty table is semantically meaningful
(https://github.com/martinvonz/jj/issues/4458#issuecomment-2407109269).
For example:
```toml
[table]
key = "value"
[another-table]
key = "value"
```
Running `jj config unset --user table.key` will leave us with `table`
being empty:
```toml
[table]
[another-table]
key = "value"
```
This addresses issue #3317, where as discussed we want to show the paths to
configuration files if they contain errors, to make it easier for the user to
locate them.
"config list NAME" argument is now parsed as TOML key, but it's still broken
since config.get() expects a query expression in different syntax.
The other config commands will be migrated later.
It's inconsistent that some warnings have headings and some don't, and it seems
the choice is arbitrary. Let's unify the style. There are two exceptions:
1. continued line following labeled message,
2. "unrecognized response" followed by prompt.
There's a caveat: "jj config list -Tname" will concatenate all names in a
single line. That's correct but useless. We might want some option or config
knob to complete missing "\n". This also applies to "log --no-graph".
this greatly speeds up the time to run all tests, at the cost of slightly larger recompile times for individual tests.
this unfortunately adds the requirement that all tests are listed in `runner.rs` for the crate.
to avoid forgetting, i've added a new test that ensures the directory is in sync with the file.
## benchmarks
before this change, recompiling all tests took 32-50 seconds and running a single test took 3.5 seconds:
```
; hyperfine 'touch lib/src/lib.rs && cargo t --test test_working_copy'
Time (mean ± σ): 3.543 s ± 0.168 s [User: 2.597 s, System: 1.262 s]
Range (min … max): 3.400 s … 3.847 s 10 runs
```
after this change, recompiling all tests take 4 seconds:
```
; hyperfine 'touch lib/src/lib.rs ; cargo t --test runner --no-run'
Time (mean ± σ): 4.055 s ± 0.123 s [User: 3.591 s, System: 1.593 s]
Range (min … max): 3.804 s … 4.159 s 10 runs
```
and running a single test takes about the same:
```
; hyperfine 'touch lib/src/lib.rs && cargo t --test runner -- test_working_copy'
Time (mean ± σ): 4.129 s ± 0.120 s [User: 3.636 s, System: 1.593 s]
Range (min … max): 3.933 s … 4.346 s 10 runs
```
about 1.4 seconds of that is the time for the runner, of which .4 is the time for the linker. so
there may be room for further improving the times.
Before this patch, it was an error to run `jj config set --user foo
'[1]'` twice. But it's only been broken since the previous commit
because '[1]' was interpreted as a string before then.
