Option to remove scientific notation from cast calls

[jordaniza]

Up until recently, cast call would return just the return data. Now a separate value is returned if the return type is specified as uint256.

I can parse this quite happily with shell commands but it's an extra headache and has broken all my scripts. Moreover the behaviour is not consistent, if you don't decode the return data, you get one value.

It would be great to make this either:

• not the default - developers can parse big numbers themselves
• opt out with a flag - breaking change but otherwise doesn't introduce new parsing logic.

[mds1]

Closing as duplicate of #6598, feel free to add any thoughts to that discussion

Also related to #6600