Fix char array setValue() using buffer size instead of string length

[Copilot]

When a char[] array is passed to setValue(), template deduction matches T = char[N] as an exact reference bind — beating the const char* overload that requires array-to-pointer decay. The template's fallback then uses sizeof(T) (the full buffer size) instead of strlen(), causing oversized transmissions or the value exceeds max error.

Changes

• src/NimBLEAttValue.h — pre-C++17 path: Added a new enable_if template overload specifically for char[] arrays (detected via std::is_array + std::is_same<std::remove_extent_t<T>, char>). Uses strnlen(s, sizeof(T)) to cap at the buffer boundary. Updated the existing generic template's enable_if condition to exclude char arrays, keeping the two overloads mutually exclusive.

• src/NimBLEAttValue.h — C++17 path: Added an else if constexpr branch in the if constexpr chain to handle char arrays before the final sizeof fallback.

Example

char str[45];
sprintf(str, "12345678901234567890A");  // 21 chars
characteristic->setValue(str);
// Before: sent 45 bytes (full buffer)
// After:  sent 21 bytes (strlen of content)

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