`Delta_timer` is an optimized two-probe group to track time differences between calls to `start` and `stop`.

`type t`````
`type state``= private Core.Time_ns.t```
`val create : name:string ‑> t`
`val start : t ‑> unit`
`val stop : t ‑> unit`
`val pause : t ‑> unit`
`val record : t ‑> unit`
`val stateless_start : t ‑> state`
`val stateless_stop : t ‑> state ‑> unit`
`val wrap_sync : t ‑> ('a ‑> 'b) ‑> 'a ‑> 'b`

Typically partially applied (the first two arguments) to produce a 'wrapped' function. This behaves like the identity function on functions, except it times the inner function.

`val wrap_sync2 : t ‑> ('a ‑> 'b ‑> 'c) ‑> 'a ‑> 'b ‑> 'c`
`val wrap_sync3 : t ‑> ('a ‑> 'b ‑> 'c ‑> 'd) ‑> 'a ‑> 'b ‑> 'c ‑> 'd`
`val wrap_sync4 : t ‑> ('a ‑> 'b ‑> 'c ‑> 'd ‑> 'e) ‑> 'a ‑> 'b ‑> 'c ‑> 'd ‑> 'e`