orders: extract work order list geometry

[Robuske]

Summary

• Extract the Work Orders list geometry calculations into plugins.orders.work_order_list so Lua overlays can share the same row positions and visible range.
• Update the existing orders search overlay to use the extracted module without changing its behavior.
• Add focused coverage for list placement, viewport sizing, and end-of-list clamping.
• Add the required changelog and contributor entries.

Testing

• Ran the targeted orders tests in a loaded fortress:

  test -d C:/Users/rodbu/Developer/Dwarf/dfhack/test -t orders
  

  Result on this branch: 10/10 tests passed, 48/48 checks passed.

• The stacked position-overlay branch also passed 14/14 tests and 78/78 checks.

[chdoc]

While we are far from consistent about this, I would prefer if new libraries were using camel case instead of snake case. This would bring local_module.someThing more in line with dfhack.module.someThing. The global API consistently uses camel case. In particular, given that most of the local imports use single words or acronyms as names.

[Robuske]

@chdoc PR has been updated to use camelCase