Disable kernel caching from within pyopencl code

**Is your feature request related to a problem? Please describe.**
When debugging an OpenCL implementation, I like to use pyopencl for my reproducers for other teams and easy testing. Since the default behavior is caching, this causes some surprises when tuning for example an OpenCL compiler, running the same code but expecting different results due to the tuning.

**Describe the solution you'd like**
Add a keyword argument to `pyopencl.Program.build(...)` called 'cached', which is a bool. If true, use caching even if `PYOPENCL_NO_CACHE` is not set, possible print a warning about this. If false, don't use caching, even if `PYOPENCL_NO_CACHE` was set, possibly print a warning about this.

**Describe alternatives you've considered**
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**Additional context**
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