refactor: clean iop APIs + add Marshal methods (#337)

* fix: vector marshal methods on pointer type

* feat: support for Vector encode / decode in Marshal

* refactor: merge Polynomial and WrappedPolynomial

* refactor: make Coefficients private and expose Slice access

* recfactor: fix constructor with []fr.Element input

* remove more apis with unexposed struct

* remove more apis with unexposed struct

* remove more apis with unexposed struct

* refactor: most consistent APIs

* style :code cleaning

* refactor: resize -> grow

* feat: added WriterTo and ReaderFrom to Polynomial

* feat: simplified putInExpectedForm

* refactor: coeffs of polynomial is no longer a pointer

* Revert "refactor: coeffs of polynomial is no longer a pointer"

This reverts commit 25425e6.

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Co-authored-by: Thomas Piellard <thomas.piellard@consensys.net>