io: name the parameter, the material and the entry when a deck is wrong (#66, #67)

[petlenz]

Closes #66, #67. Partially addresses #65 (see below).

Three failures that named nothing useful.

A wrong parameter type was a bare bad_any_cast (#65)

get_parameter() let std::bad_any_cast escape: no parameter, no material, no type, and not a class a caller would think to catch. Writing 1 where 1.0 is read -- an int for a double, which both JSON and C++ make easy -- produced bad any_cast and nothing else, at construction, before the material could say anything about itself.

set_parameter() already wrapped this. get, which every material calls several times, did not.

One reader served two different parameters (#66)

The JSON reader registry is keyed on std::type_index alone. block_ref is std::pair<std::string, std::string>, so vector_newton's zero_blocks and weighted_sum's terms are the same C++ type and resolve to the same reader. A malformed weighted_sum term reported

zero_blocks: each entry must be a [row, column] pair

naming a parameter of a different material.

Readers now receive the parameter key -- it was already available at the read() call site and thrown away -- so the shared reader names whatever it was actually given. add_for_key() lets one parameter keep its own wording without disturbing the other user of the type, so zero_blocks still says [row, column].

Any future pair of parameters sharing a C++ type would have hit the same thing.

"type" errors were a dead end (#67)

A missing "type" surfaced nlohmann's own key 'type' not found, from a library the user never named, with no indication of which entry was at fault. A misspelt one echoed the name back with no candidates.

Both now name the entry by its "name", and an unknown type suggests the nearest registered one (j2_plasticty -> j2_plasticity) or lists them all when nothing is close.

Not fixed here

#65 also covers a misspelt optional key being ignored silently in the C++ path. parameter_handler exposes no way to enumerate its keys -- only find() and print() -- so comparing a handler against a schema needs a numsim-core change. I have left #65 open for that half rather than closing it.

Tests

tests/test_parameter_diagnostics.cpp, 10 tests. 310/310.

mutation	result	killed by
get_parameter const-ref overload unwrapped	CAUGHT	BothGetParameterOverloadsReportTheSameWay
get_parameter rvalue overload unwrapped	CAUGHT	3 tests
reader key threading reverted	CAUGHT	AMalformedWeightedSumTermDoesNotMentionZeroBlocks
missing-"type" check removed	CAUGHT	AMissingTypeKeyDoesNotLeakTheJsonLibrary
unknown-type check removed	CAUGHT	3 tests

get_parameter is overloaded on how the key arrives and materials use both -- a string literal binds to the rvalue overload, a stored std::string to the const-reference one. My first version of the test reached only one, so deleting the other's guard left the whole suite green. That survived mutant is the only reason I found it; the test now drives both.