Use Fixed FileDescriptors

[manticore-projects]

libUring allows to register Files, Pipes and Buffers. The benefit is remarkable, please see simple benchmark below.

• libUring based copy with fixed files is on par with CoreUtils cp
• same code without registering the files is much slower (factor 3)

[manticore-projects]

So I think its quite important to adopt fixed files and buffers into JUring and I have mapped the required methods already in my branch.
My next step was wrap the full splice fixed files example into Java and check how it performs.

[manticore-projects]

I got Zero Copy File transfer with Pipes and Fixed File descriptors working in Java: https://github.com/manticore-projects/JUring/blob/8ce605afbd45b3a2caf15f012ddba96f89b7e2f8/src/test/java/com/davidvlijmincx/lio/api/JUringTest.java#L289

[davidtos]

The 3x performance is really something! Thanks for adding the benchmark and nice work implementing the zero-copy transfer with pipes and fixed descriptors.