Add rlimit support in fixedpoint parameters (#9798)

The C++ implementation of the fixedpoint engine (in
z3/src/api/api_datalog.cpp) already attempts to read `rlimit` from its
local parameters:

```c++
unsigned rlimit = to_fixedpoint(d)->m_params.get_uint("rlimit", mk_c(c)->get_rlimit());
```

However, because `rlimit` was not registered in the public fp parameter
schema (`fp_params.pyg`), any attempt by clients to set it locally via
`Z3_fixedpoint_set_params` was rejected by the Z3 parameter validator
with an "unknown parameter" error.

src/muz/base/fp_params.pyg

@@ -3,6 +3,7 @@ def_module_params('fp',
                   export=True,
                   params=(('engine', SYMBOL, 'auto-config',
                            'Select: auto-config, datalog, bmc, spacer'),
+                          ('rlimit', UINT, 0, "deterministic resource limit (0 means no limit)"),
                           ('datalog.default_table', SYMBOL, 'sparse',
                            'default table implementation: sparse, hashtable, bitvector, interval'),
                           ('datalog.default_relation', SYMBOL, 'pentagon',