Add utility functions and tests to signed integers

[chlenc]

Type of change

• Bug fix
• New feature

Changes

The following changes have been made to I128 and I256:

• added functions

fn from_u64(value: u64) -> I128
fn as_u64(self) -> u64
fn flip(self) -> Self
fn ge(self, other: Self) -> bool
fn le(self, other: Self) -> bool
fn zero() -> I128

• A tests
• Added check to test not to be failed

The following changes have been made to I8, I16, I32 and I64:

• added functions

fn flip(self) -> Self
fn ge(self, other: Self) -> bool
fn le(self, other: Self) -> bool

• A tests
• Added check to test not to be failed

Notes

But my tests are still failing because of the problem I have mentioned before in this topic
https://forum.fuel.network/t/cannot-use-from-uint-in-the-i128-from-sway-libs/1255

[supiket]

These are my comments for this stage of the work, but since this PR is a work in progress, I will convert this open PR to draft. I also edited the title to reflect that these changes are implemented for all signed integer types. You can mark it ready for review (open) once functions for other types and tests for all the new functions are added.

[supiket]

Suggested change

	}
	}

[chlenc]

🫡

[supiket]

Same suggestion for other instances of this, for readability purposes.

Suggested change

	let params = TxParameters::new(Some(1), Some(10000000), None);
	let params = TxParameters::new(Some(1), Some(10_000_000), None);

[supiket]

The underscore is used for unused variables.
Same suggestion for other instances of this usage.

Suggested change

	let _result = instance.main().tx_params(params).call().await;
	assert_eq!(_result.is_err(), false);
	let result = instance.main().tx_params(params).call().await.unwrap();
	assert!(result.value);

[CLAassistant]

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