Convtools

**Misc**

- locked CI dependencies
- switched packaging to hatch
- dropped setup.py and setup.cfg in favor of pyproject.toml

**Bugfix**

- fixed `c.group_by` for cases with input_arg/label inside and
iter/as_type/sort/tap methods called on it

**Bugfix**

- fixed `c.group_by` for cases where group by keys are generated functions
(e.g. deep attr lookup with default). No worries about silent errors, it used
to fail hard.

**Bugfix**

- fixed `Table.join` for cases where the right part has internal row type
different from the left one

**Features**

- introduced `c.iter_unique(element_conv=None, by_=None)` and
`(...).iter_unique` methods which define a conversion, which iterates over
the input and yields values unique based on the provided condition

**Features**

- introduced `c.date_parse` / `c.datetime_parse` shortcut and extension of
`datetime.strptime`
- introduced `c.date_trunc` / `c.datetime_trunc` to truncate dates to years,
months, days-of-week, etc. (including multiples of them like quarters -
`3mo`). Support offsets.
- introduced `DateGrid` / `DateTimeGrid` helpers to build gap-less series of
dates/datetimes. Support offsets.