Enhance radixtree_uri_with_parameter to automatically differentiate literal segments from path parameters

### Description

The current radixtree_uri_with_parameter router cannot distinguish a literal segment from a parameterised one. (APISIX version: 3.14.1)
For example, with the following routes:

GET /user/comn-language/:tenantId/all
GET /user/comn-language/:tenantId/:langId

and the request /user/comn-language/123/all, the router cannot determine accurately which route to match unless a priority field is manually set it picks the GET /user/comn-language/:tenantId/:langId route
The router should be enhanced with a built‑in precedence rule: a literal segment always wins over a parameter placeholder when both could match the same request.

Start by tracing the radixtree_uri_with_parameter router and reproduce the two routes with /user/comn-language/123/all. The work is done when a literal segment takes precedence over a parameter placeholder without manually setting priority, with a regression test covering the example.

Written by the indexing model from the issue text.