fix: detach not invoke delete lifecycle

[AFutureD]

This PR is aiming to fix the issue #533 and vapor/fluent#747.

The SiblingsProperty.detach(_:on:) miss to invoke delete lifecycle, while SiblingsProperty.attach(_:on:) does.

The last line .delete() just simply build an sql and runs it, which cause some issues.

    public func detach(_ tos: [To], on database: Database) -> EventLoopFuture<Void> {
        guard let fromID = self.idValue else {...}
        let toIDs = tos.map {...}

        return Through.query(on: database)
            .filter(self.from.appending(path: \.$id) == fromID)
            .filter(self.to.appending(path: \.$id) ~~ toIDs)
            .delete()
    }

[0xTim]

I think we're going to have to be a bit cleverer here and manually invoke the lifecycle or similar because at the moment we can't accept the patch as is as it turns a functions that performs one SQL query into a function that performs as many queries as there are siblings which would be a big performance hit

[0xTim]

cc @gwynne

[AFutureD]

Agreed. This PR does have some potential performance issues. But, it might be a little difficult to figure out the cleaver solution. Waiting for your idea.

[AFutureD]

If we could get all models first, and then invoke lifecycle manually.
After that, we delete as before.

@0xTim Is it an option?

Pseudocode may as follows:

let query = Through.query(on: database)
            .filter(self.from.appending(path: \.$id) == fromID)
            .filter(self.to.appending(path: \.$id) ~~ toIDs)

try await query.all().map { $0.invoke() }

try await query.delete()

[0xTim]

Unfortunately that still loads potentially a very large number of pivots in to memory which can be slow. I'm going to defer to @gwynne when she gets a chance to look at it as it's her codebase and she's the expert on all things Fluent