Fix integer precision loss and unused function warnings when using Hardened Compiler Flags

- Marked the `VerifyOperatorAttributeAndInputs` function as [[maybe_unused]] to avoid warnings.
- Replaced `size_t` with `uint32_t` in multiple loops across `tosa_serialization_handler.cpp` and `serialization_npy_test.cpp` for type consistency.
- Applied `static_cast<uint16_t>` and `static_cast<int8_t>` where necessary to ensure safe and explicit type conversions.

Change-Id: Ic22222c6b8736f953339f86b3848dadbc4ce37dc
Signed-off-by: Yuvaraj Venkatesh <yuvaraj.venkatesh@arm.com>