use build.zig instead of build.sh

[andrewrk]

In order to merge this, some more steps are needed:

1. Support fetching dependencies over git+http(s) ziglang/zig#17277 needs to land in zig
2. add the build.zig logic for building the orca tool itself (if orca upstream used build.zig then we could just grab the exe from there)
3. testing

for step 2, since the orca tool depends on python, this will reduce system dependencies down to only python. alternately python could be provided by zig build but that may be a bit extreme, might be better to just have a system dependency on python, because I think the orca devs might decide to eliminate that dependency eventually.

Why do this?

• the project already depends on zig, so let's use it for the build system instead of an additional dependency on shell scripting (which does not work on Windows)
• no need to fiddle with ORCA_DIR, zig build can set everything up for the user so they can get started with only running zig build

[andrewrk]

ziglang/zig#17277 has landed in zig, however ziglang/zig#16678 is also a blocker for this PR since the orca source tree uses symlinks.

[kristoff-it]

lgtm