[$] The first half of the 6.7 merge window

As of this writing, 9,842 non-merge changesets have found their way into
the mainline repository since the 6.7 merge window opened. Nearly a third
of those consist of the entire bcachefs development history but, even
discounting that, there has been a lot of material landing for the next
release. Read on for a summary of the most interesting changes pulled so
far in this development cycle.