Cleanup pass: dead code, needless copies, and a few small fixes

[marekl11]

Mostly a cleanup pass over the plugin's own code (ThirdParty untouched), with a few small bugs I ran into while doing it. No behaviour changes beyond the fixes listed below.

Cleanup

• ToSIOMessage copied the whole FJsonObject::Values map on every object emit — auto on a TMap deduces to a copy. Also made the range-for loops take their pairs by reference, and StdString/FStringFromStd take const& instead of by value.
• Dropped [&] from ten lambdas that already capture everything they use explicitly. The ones that genuinely reach for a member are left alone, so it's now visible which those are.
• Removed the unused condensed-writer typedefs and their two includes, a commented-out declaration in the module, a dead CastField stub in SocketIOFunctionLibrary, and two #pragma endregion with no matching region.
• ReplaceJsonValueNamesWithMap was serializing the whole subtree to a string at every object level to feed two commented-out log lines.

Fixes

• Break Json is unusable. All three sites resolve the pin class via StaticLoadObject("class'SIOJPlugin.SIOJJsonObject'") — a module and class name from before the module split. The load returns null, Compile() dereferences it, and compiling a Blueprint containing the node takes the editor down. Now uses USIOJsonObject::StaticClass(); SIOJson is already a public dependency of that module.
• Conv_CompactBytesToTransforms / Conv_CompactPositionBytesToTransforms write past the array. Both size a float view for Num()/4 floats and then memcpy Num() bytes into it before the divisibility check. Any input that isn't a multiple of four writes the trailing bytes out of bounds, and these are Blueprint-callable on network-supplied bytes. Moved the length check ahead of the copy.
• SplitFullPath's backslash fallback can't match. It splits on TEXT("\\\\"), which is the two-character string \, so a Windows-style path never splits and both out params keep whatever the caller had — SaveBytesToPath then fails on the empty path.
• EncodeJsonToSingleString does nothing. Both Replace calls discard their result (Replace returns a new string), and the second searches for LINE_TERMINATOR while its comment says "remove tabs" — once assigned it would have inserted a tab per line break.
• GetBinaryField is missing two guards. No JsonObj.IsValid() check, unlike every other accessor in the file, and it logs a type mismatch without returning. FJsonValueBinary::IsBinary is also true for array, object and null values, so the unchecked downcast below reads a TArray member that isn't there.
• ToSIOMessage built std::string(nullptr, 0) for an empty binary value.
• ENABLE_CUPRECISE_TIMER was #defined unconditionally, so Tock's #else branch could never compile and the off mode didn't exist. Wrapped in #ifndef.

One naming change

FSocketIONative::kUnlimitedReconnectionAttempts. The component initialised MaxReconnectionAttempts from a float literal (-1.f) into an int32, the native used a bare -1 into a uint32, and the header said "0 = infinity" — but sio compares m_reconn_made < m_reconn_attempts on an unsigned, so 0 means zero attempts and only the -1 wraparound made the default unlimited. Nothing changes at runtime; it just says what it means, so a later tidy-up doesn't turn reconnection off.

Happy to split any of this out if you'd rather take it in pieces.