Add linter checks to GHA & Fix code to pass lints.
The linters added are:
- whitespace: Tool for detection of leading and trailing whitespace
- gosec: Inspects source code for security problems
- gci: Gci control golang package import order and make it always deterministic
- misspell: Finds commonly misspelled English words in comments
- gomnd: An analyzer to detect magic numbers

The file utils/utils.go is excluded from the checks of gomnd, as uses magic numbers through the code

* 16 bits fix encoding

* Types modification

* Rounding loss check

* Clean up a bit and add benchmarks

Unneded usage of big.Int has been removed

Conversion methods are now methods/constructors of Float16 to make the code
more idiomatic.

Co-authored-by: Toni Ramírez <toni@iden3.com>
Co-authored-by: arnaucube <root@arnaucube.com>
Co-authored-by: Eduard S <eduard@iden3.io>