This PR fixes issue with incorrect handling of head trits in flex_trits_insert_from_pos. It affects iota_pow_flex.
Also, fixed the test case for iota_pow_flex as it used sizes in flex trits instead of trits which results in invalid behaviour of iota_pow_flex, iota_flex_digest and flex_trits_to_trytes in the test case.
This PR fixes issue with incorrect handling of head trits in
flex_trits_insert_from_pos. It affectsiota_pow_flex.Also, fixed the test case for
iota_pow_flexas it used sizes in flex trits instead of trits which results in invalid behaviour ofiota_pow_flex,iota_flex_digestandflex_trits_to_trytesin the test case.