Allow summarisers inside the row group header

[andyov17]

Currently a summariser always shows at the end of a row group, but it can end up looking quite duplicated.
For example in the filament demo here, you see the rows:

Order date: May 4, 2024 ⌃
OR673129 | Tania Rice | Processing | Australian Dollar | 444.46 | 118.01
May 4, 2024  summary                                   | 444.46 | 118.01

I would like to suggest we have the ability to combine so it would look like

Order date: May 4, 2024 ⌃                              | 444.46 | 118.01
OR673129 | Tania Rice | Processing | Australian Dollar | 444.46 | 118.01
                           

As per screenshot mockup below

Not sure how difficult this would be to implement. Summaries are always at the bottom which may be difficult to change

[quint-pruijssers]

+1 for this. We ran into the same thing in a financial reporting table grouped by category, where every group needs its totals (cost, subtotal, margin). Basically the same as the mockup above.

The trailing summary row didn't really work for us. With a lot of small groups, you almost double the number of rows, and it just looks like duplicated data. And when a group is collapsible, the totals disappear together with the rows, while a collapsed group with only its totals is exactly the view our users want.

I ended up building this as an opt-in Summarizer::inGroupHeader() method, see #20229. You set it per summarizer, so you can put some totals in the header and keep others at the bottom. The trailing summary row only disappears if nothing is left in it, so nothing changes if you don't use it.

While working on that reporting table, I hit two more things in the same corner and built those as well:

• Summaries can only render below the records. On long tables you scroll past everything before you see the totals, while the totals are the main thing people open the page for. feat(tables): allow summaries to be positioned at the top of the table #20227 adds ->position(SummarizerPosition::Top) per summarizer, so you can put some totals above the records and keep others below. Default stays bottom.
• Group headers are always gray. In our table one special group has to stand out from the normal category groups, and with many groups a bit of color makes scanning a lot easier. feat(tables): add color support to table groups #20228 adds Group::make('status')->color('info') (or a closure that gets the first record of the group). null keeps the current styling.

All three PRs got closed because there wasn't enough demand yet, so if you need any of this, an upvote here probably helps. Happy to pick them back up if that changes.