Parameter errors name neither the parameter nor the material: bad any_cast, ignored keys, truncated numbers

[petlenz]

Several parameter mistakes produce either an unusable message or none at all.

Mistake	What happens
int where a double is expected (C++ path)	bare std::bad_any_cast, names nothing
misspelt optional key (C++ path)	silently ignored; the JSON path warns
"max_iter": 7.9	silently truncated to 7
missing required parameter	C++: names one of several; JSON: names none. Never names the material

numsim-core already provides check_data_type (-> Parameter 'K' has wrong type) and range<Min, Max>. No material uses either.

Fix

• attach check_data_type when a parameter is declared, so it applies to every material at once rather than per material;
• reject unknown keys in the C++ path the same way the JSON path warns;
• reject a non-integral value for an integer parameter;
• wrap parameter errors at the material boundary so the message carries the material name and type (numsim-core cannot know these). The missing-names half is tracked in Missing-parameter error reports a count, not the parameter names numsim-core#20.

All references are to main at 91bd26f.