add cache table to track caches

[swelborn]

we need a cache reegistry so that later we can explicitly shut the cache down. we need to be able to track these by experiment, so we can query to see what caches are up for the experiment

later, we could move away from “experiment” as the key and have a more generic key for the shared cache.

we also need this table to lock the row before deleting. otherwise we would end up in a situation where we get another request for an experiment transfer on the cache it will race. while this is probably not going to happen often we should still have it.

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This is part 19 of 23 in a stack made with GitButler:

•  23  use historical=True as a fallback if job not found #52
•  22  test coverage for credential boundary #51
•  21  remove "force" option for cache shutdown #50
•  20  client/service/workflow changes for IRI token delegation changes #49
•  19  add cache table to track caches #48 👈
•  18  authenticated principal + encrypted delegated-credential capture #47
•  17  OIDC transfer ownership and delegated user credentials #46
•  16  WIP for shared cache shutdown #45
•  15  add jobspec override #44
•  14  add mostly claude-gen usage example package #43
•  13  ability to share a cache amongst different transfers #42
•  12  add precommit hook for checking openapi client drift #40
•  11  pin python version to 3.14 #41
•  10  build frontend image in CI #39
•  9  add frontend #38
•  8  add frontend client (autogenerated) #37
•  7  lazily construct settings #36
•  6  add autogenerated client #35
•  5  add alembic #34
•  4  add ability to get logs from v2 api services thru iri #29
•  3  functional core tests for transfer and producer #30
•  2  api with durable execution and saga #28
•  1  deps for v2 #27