The key-loop unconditionally called self.parse() and overwrote
result.children[key] for literal segments after the walk-down loop
broke at a parameter. This destroyed pre-existing subtrees (with their
method children and handlers) when a second route (e.g. POST) shared
the same literal sub-segments after a parameter.
Added a children.get(key) reuse check before parse(), mirroring the
walk-down loop's child-reuse logic but extended past the boundary
where parameters live in path_matchers, not children.
When two routes share the same parameter at the same node position
(e.g. GET /restaurants/${id} and GET /restaurants/${id}/menu),
reuse the existing equivalent matcher instead of raising a conflict.
Non-equivalent matchers (different names, kinds, or glob patterns)
at the same node for the same method still raise ValueError.
woggioni