Align OraParam walker callback typing with tree-walker conventions

raw_calculate_oraparamnumbers_walker() used a legacy callback type
(bool (*)()) that relies on non-prototype function semantics. Newer
Clang warns on each recursive callback call when warnings are treated as
errors.

Build error excerpt:

```
../src/backend/parser/parse_param.c:773:14: error: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C23
[-Werror,-Wdeprecated-non-prototype]
```

Switch the callback to tree_walker_callback and route recursive calls
through a local WALK() macro so this walker matches PostgreSQL
conventions and compiles cleanly under strict warning settings.

Author: c2main