More checks on numeric input for zstd CLI

[IAL32]

Closes #3070

• Added check for a possible invalid combination of numeric values in zstd CLI
• Does not perfectly cover all invalid combinations, but it's better than before
• Added some tests
• Slightly changes --memory, --memlimit and --memlimit-decompress to only be used with = at the end of the parameter
• memLimit type changed from unsigned to size_t to be more in line with srcSizeHint, as both refer to memory values

[Cyan4973]

Issue fixed in #3268