Benchmarks; Direct access to PJRT Buffers (when using CPU); Several speed ups.

• Added install_linux_amd64_amazonlinux.sh and pre-built libraries for amazonlinux (built using old glibc support).
• Fixed installation scripts: s/sudo/$_SUDO. Also made them more verbose.
• Removed dependency on xargs in installation script for Linux.
• Improved documentation on Nvidia GPU card detection, and error message if not found.
• Updated GitHub action (go.yaml) to only change the README.md with the result of the change, if pushing to the
  main branch.
• Added prjt.arena to avoid costly allocations for CGO calls, and merged some of CGO calls for general speed-ups.
  The following functions had > 50% improvements on their fixed-cost (measured on transfers with 1 value, and minimal programs)
  execution time (not the variable part):
  • Buffer.ToHost()
  • Client.BufferFromHost()
  • LoadedExecutable.Execute()
• Added BufferToHost and BufferFromHost benchmarks.
• Added support for environment variable XLA_DEBUG_OPTIONS: if set, it is parsed as a DebugOptions proto that
  is passed to the JIT-compilation of a computation graph.
• LoadedExecutable.Execute() now waits for the end of the execution (by setting
  PJRT_LoadedExecutable_Execute_Args.device_complete_events).
  Previous behavior lead to odd behavior and was undefined (not documented).
• Package dtypes:
  • Added tests;
  • Added SizeForDimensions() to be used for dtypes that uses fractions of bytes (like 4 bits).
• Added Client.NewSharedBuffer (and the lower level client.CreateViewOfDeviceBuffer()) to create buffers with shared
  memory with the host, for faster input.
  • Added AlignedAlloc and AlignedFree required by client.CreateViewOfDeviceBuffer.
• Added Buffer.Data for direct access to a buffer's data. Undocumented in PJRT, and likely only works on CPU.
• Fixed coverage script.