Fuse quadrule and momintegrals! into integrate! to avoid dynamic dispatch

[djukic14]

momintegrals! is renamed to integrate!. The quadrule methods used by
IntegralOperator assembly (dispatching on AbstractQuadStrat) now build
their quadrature rule and call integrate! on it directly, from within
the same method/branch, instead of returning it to assemblechunk_body!
for a separate call.

Which behavior results is controlled by a new action keyword:

• action=ApplyIntegrate() (default) evaluates the rule
• action=ReturnQRule() returns the rule unevaluated, e.g. for
  quadinfo (which now returns the rule instead of nothing)
• action=ApplyIntegrateNonConforming() is used by
  NonConformingOverlapQRule/NonConformingTouchQRule, whose integrate!
  methods only have local refspaces in scope, not a full Space

quadrule methods outside this family (LocalOperator, excitations,
farfield/nearfield postprocessing) are untouched and keep their name.

Adds test/test_quadrule_integrate_dispatch.jl, an allocation-based
regression test proving the fusion avoids the union-boxing that the
old two-step call pattern incurred.

Updates CHANGELOG.md and the quadrule/quadstrat/assemble docs to
match, including docstrings for the new action types and integrate!/
quadrule/quadinfo.

I’m happy to discuss the naming and adjust it as needed.
The solution for NonConformingOverlapQRule / NonConformingTouchQRule isn’t quite as elegant, but it’s the best approach I came up with.