fix #496: add concore.java for local Java nodes

[avinxshKD]

Java had concoredocker.java but nothing for local file I/O, couldn't
run a Java node without Docker. This adds concore.java (mirrors concore.py)
and updates mkconcore.py to recognize .java files and generate the right
build/run/debug scripts for Windows and POSIX.

• concore.java, file-based read/write, PID registry + kill script (Windows),
  ZMQ support, literal eval parser
• mkconcore.py, java in lang validation, docker/local switch in required_langs
  block, javac in local build + POSIX run scripts

fixes #496

[avinxshKD]

Hey @pradeeban added the missing library + mkconcore.py support for build/run/debug on
both Windows and POSIX

Also no tests yet, kept it minimal for now.... should I mirror TestConcoredockerApi.java for this? or keep it for later.

Java's been a second-class citizen here for a while. I hope not a toy anymore :)

[avinxshKD]

Also @pradeeban, @Rahuljagwani, @mayureshkothare,

Been about 2-3 weeks heads-down on this.... taking a bit longer than expected but wanted it to be solid before sending. Will have the draft proposal to you in the next day or two.

A few things I wanted to know and guided by you.... before I finalize:

1. For benchmarks, planning the scripts (file vs mmap vs ZMQ, Julia vs Python) as a week-9 deliverable. Research note writeup kept optional since the quality depends on how clean the numbers turn out. Does that match what you had in mind?

2. Added a section arguing for native reimplementation over a PyCall wrapper, Python dep chain, no dispatch, marshaling overhead per cycle, messy Pkg registration. Every other concore language has a native impl. Does that hold technically

3. If mentors are open to it, preparing Concore.jl for Julia General Registry submission, either via subdirectory registration from the main repo or a standalone package repo. This one depends on how the org wants to structure things, so it's a conversation, not just a coding task. (would it be okay to add this as a stretch goal in "if time permits")

[pradeeban]

@avinxshKD 1. I think the "research note" as in measuring/benchmarking can be a core part of the GSoC. But refining to publish as a research paper is usually something beyond the scope of GSoC. (We cannot use GSoC as a primarily research paper writing task, as GSoC is meant to be a coding task). The distinction is documentation+evaluation (a core component of software development) vs. a research paper draft (not a core component of software development).
2. Yes.
3. Sure.

Good work.

[pradeeban]

@avinxshKD

Looks like too many unnecessary line changes in mkconcore.py whereas the actual line changed was just one line.

Can you remove all the unnecessary line changes in this file, keeping the changes to that file to bare minimum?