Random allocation could pick 33646 = admin.port (23646) + GrpcPortOffset.
weed mini reserves that as Admin's gRPC port even when the test only
overrides Master/Filer/S3/Iceberg, so the explicit Filer flag failed
with "reserved for gRPC calculation" and TestRisingWaveIcebergCatalog
flaked. Pre-seed the reserved set with every mini default HTTP port
plus its +10000 offset so a random pick (or its own gRPC offset) cannot
land on a service the caller left at its default.
AllocateMiniPorts(1) reserved masterPort and masterPort+GrpcPortOffset
by holding listeners open, but closed them on return. The subsequent
AllocatePorts call bound 127.0.0.1:0, so the OS could immediately reuse
the just-released mini gRPC port as a volume port — causing the volume
server to fail at bind time with "address already in use".
Introduce AllocatePortSet(miniCount, regularCount) that holds every
listener open until the full set is chosen, and route the five volume
test cluster builders through it.