Introduce Big Integers Library

[bitzoic]

Type of change

• New Library

Changes

The following changes have been made:

• Introduces the Big Integers Library with the BigUint type

The BigUint type has the following functions:

• new()
• equal_limb_size()
• number_of_limbs()
• limbs()
• get_limb()
• zero()
• is_zero()

The following traits are implemented for the BigUint type:

• Clone
• From<u8>
• TryInto<u8>
• From<u16>
• TryInto<u16>
• From<u32>
• TryInto<u32>
• From<u64>
• TryInto<u64>
• From<U128>
• TryInto<U128>
• From<u256>
• TryInto<u256>
• From<Bytes>
• Into<Bytes>
• Eq
• Ord
• OrdEq
• Add
• Multiply
• Subtract

Notes

• Until this PR is merged, CI link check will error with:

ERROR: 1 dead links found!
  [✖] https://fuellabs.github.io/sway-libs/master/sway_libs/bigint/index.html → Status: 404 

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.
• I have updated the changelog to reflect the changes on this PR.

[K1-R1]

Overall looks great, a few suggestions then very happy to approve

[K1-R1]

Suggested change

	The Big Integers Library offers a number of different conversion between mathematical type. These include the following:
	The Big Integers Library offers a number of different conversions between mathematical types. These include the following:

[K1-R1]

Suggested change

	The [Big Integers](./bigint/index.md) Library is an interface to implement extremely integers.
	The [Big Integers](./bigint/index.md) Library is an interface to implement extremely large integers.

[K1-R1]

Suggested change

	/// Returns the number of limbs the `BigUint`.
	/// Returns the number of limbs the `BigUint` has.