InventoryWorker

The thread side of `InventoryService`: it owns the sampler and every `/proc` read the inventory makes (monitor-async-sampling §MSA-C-5).

In the namespace inventory. Declared in src/libs/libinventory/inventory/InventoryWorker.hpp.

Detailed description

The sampler is stateful, and its rates are deltas against the previous sample, so one thread owns it and nothing else touches it. The service only requests and receives.

A full sample for a client of the service (the Monitor screen) runs through a `SamplerWorker` on this thread, over the same sampler, so both read one set of deltas. Each full sample also gives a `NodeLoad`, and moves the interval sample one and a half of the client's periods later. So a sampler that a client drives is not also read on the interval, and the client's rates cover its whole column; the interval sample comes back only when the client stops asking.