re_datastore: all around performance pass tracking issue

[teh-cmc]

First pass of performance work

• put performance probes everywhere
• provide helpers to gather detailed metrics: global, per-table, per-table-per-bucket
• a lot superfluous clones & copies that need to go away asap
• need integration benchmark suites
  • write path, read path, write+read path

The end game, of course, is that query results from the datastore should always be references to the stored data.

And all of the following:

• re_datastore: properly handle already sorted data during insertion #433
• re_datastore: implement efficient reshuffling on the read path #442
• re_datastore: get rid of immutable arrays in component buckets #451
• re_datastore: optimize backwards walk in read path #453
• re_datastore: IndexTable::latest_at early-exit on unknown component #529

Optional:

• re_datastore: small-list optimization (aka. component inlining) #448

[emilk]

Let's just add some probes this cycle