Verify that gas costs are always positive, or handle it correctly.

[JulianGCalderon]

In the metadata::gas module, we are panicking if the function costs is negative, in multiple places, but the actual data type is a signed integer.

cairo_native/src/metadata/gas.rs

Line 99 in ac3e1a4

TryInto::<usize>::try_into(*val)

We should handle the case of a negative gas cost, either by returning a Native Assert in case its impossible, or handling it in case its possible.

See the Native Assert module definition on instructions on how and why to use it:

cairo_native/src/error.rs

Lines 133 to 138 in ac3e1a4

	/// In Cairo Native we want to avoid the use of panic, even in situation where
	/// it *should* never happen. The downside of this is that we lose:
	/// - Possible compiler opitimizations
	/// - Stack backtrace on error
	///
	/// This modules aims to avoid panics while still obtaining a stack backtrace on eventual errors.