Parametrize pow in stdlib field and update keccak

[Rumata888]

barretenberg/cpp/src/barretenberg/stdlib/primitives/field/field.cpp

Line 357 in 97c9bc7

field_t<ComposerContext> field_t<ComposerContext>::pow(const field_t& exponent) const

Pow always uses 32-bit exponent which can sometimes be a waste. We should parametrize this function to allow different expected maximum exponents