Add nativeIO for madvise on mapped page cache

[dstuebe]

Changes:

• Add c build step for jni
• Add nativeIO madvise system call wrapper
• Advise page tables and headers as 'will use'
• Add option to advise blob pages as 'random'
• Use mapped pages for writing in virtual pages files

Local benchmarking shows little impact on IO performance from use of madvise - this is good as impact might have been negative. Need to test under memory pressure at high IO in production environment. It would be ideal to develop a more rigorous local test with memory pressure.

The write to mapped change is an unexpected benefit. Need to test carefully in production as we have gone back and forth on this as a best practice. It looks like the latest iteration is a clear win for mapped IO as the benchmark time is cut in half!

See https://stackoverflow.com/a/49500154/2136991 for packaging & loading the dynamic library

[codecov-io]

Codecov Report

Merging #108 into master will decrease coverage by 0.59%.
The diff coverage is 70.58%.

@@             Coverage Diff             @@
##             master     #108     +/-   ##
===========================================
- Coverage     89.76%   89.17%   -0.6%     
- Complexity      723      724      +1     
===========================================
  Files            56       57      +1     
  Lines          2688     2725     +37     
  Branches        177      178      +1     
===========================================
+ Hits           2413     2430     +17     
- Misses          191      211     +20     
  Partials         84       84

Impacted Files	Coverage Δ	Complexity Δ
...va/com/upserve/uppend/blobs/VirtualPageFileIO.java	83.33% <ø> (ø)	20 <0> (ø)	⬇️
...c/main/java/com/upserve/uppend/blobs/FilePage.java	100% <ø> (ø)	5 <0> (ø)	⬇️
src/main/java/com/upserve/uppend/BlockedLongs.java	82.68% <100%> (-0.24%)	52 <1> (-3)
...ava/com/upserve/uppend/AppendOnlyStoreBuilder.java	100% <100%> (ø)	14 <2> (+2)	⬆️
.../java/com/upserve/uppend/cli/CommandBenchmark.java	96.15% <100%> (+0.15%)	6 <0> (ø)	⬇️
.../java/com/upserve/uppend/AppendStorePartition.java	87.82% <100%> (+0.1%)	20 <0> (ø)	⬇️
...c/main/java/com/upserve/uppend/blobs/NativeIO.java	36.66% <36.66%> (ø)	1 <1> (?)
...java/com/upserve/uppend/blobs/VirtualPageFile.java	82.2% <96%> (-0.18%)	61 <12> (+1)

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[dstuebe]

Got the dylib included in the Jar - but I can't get the build to or load to support multiple targets (linux & mac)
It loads automatically from the jar but only assuming the target platform is mac (dylib not so)
Jitpack build fails - apparently they don't support native build - no gcc/clang?

[dstuebe]

Frustrated with integration for JNI - difficult to build multiple targets, jitpack does not support at all.

Investigating use of JNR-FFI but use of constants is a bit kludgy investigating adding madvise values there.

[dstuebe]

Closing based on revised implementation using JNR-FFI in #109