Add primitive conversions submodules to the prelude

[bitzoic]

Description

As part of #6087, it was revealed that the current use std::primitive_conversions::*; line in the prelude does not import anything which a developer can use. To use any of the submodules in the primitive conversions library, users would need to import the individual submodule regardless of the prelude.

This PR adds the submodules as an import to the prelude to stay consistent with the original intent. Both the core's and std-lib's primitive conversions modules are imported. Conversions between primitive types should not require additional imports.

Example before:

use std::primitive_conversions::u32::*;

fn foo() {
    let my_u8 = 1_u8;
    let my_u16 = 1_u16;
    let my_u64 = 1_u64;

    let u32_1 = u32::from(my_u8);
    let u32_2 = u32::from(my_u16);
    let u32_3 = u32::try_from(my_u64);
}

Example after:

fn foo() {
    let my_u8 = 1_u8;
    let my_u16 = 1_u16;
    let my_u64 = 1_u64;

    let u32_1 = u32::from(my_u8);
    let u32_2 = u32::from(my_u16);
    let u32_3 = u32::try_from(my_u64);
}

Closes #6088

Dependent on #6087

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.