Optimize InvocationContext creation & sharing among composite handlers

[schlosna]

Avoid multiple calls to System.nanoTime() to avoid unnecessary overhead.

See also https://shipilev.net/blog/2014/nanotrusting-nanotime/

[schlosna]

Will likely require injecting nanos into handler preInvocation and API break

[schlosna]

While at it, really need to inject ticker for testing

[carterkozak]

Rather than optimization on sharing data, perhaps we could solve this with additional isolation? #393