refactor(gstd): align gstd reexports & prelude items with std

[fluiderson]

In gstd's prelude module, the following is stated:

gear/gstd/src/prelude.rs

Lines 19 to 20 in fdb21be

	//! The `gstd` default prelude. Re-imports default `std` modules and traits.
	//! `std` can be safely replaced to `gstd` in the Rust programs.

That's not entirely true. Several modules and types, which can be found in std's prelude module, are missing in gstd's one. So, in this PR, I refactored the prelude module to make gstd align to std as much as possible.

The only problem here is that I'd like to leave reexports in this format for easier alignment maintaining with std, but rustfmt is configured to merge use statements. For now, I removed imports_granularity = "Crate" from rustfmt.toml, but the final solution needs to be discussed.

[ark0f]

For now, I removed imports_granularity = "Crate" from rustfmt.toml, but the final solution needs to be discussed.

The line should not be removed for the whole repo because we have requirement to merge imports. It was done manually via PR author or reviewer request before.

For now I can offer to apply #![rustfmt::skip] attribute or introduce module + reexport with #[rustfmt::skip] applied.

Also, as @grishasobol said, I'm not sure we actually need to follow line by line as in std::prelude and I guess it can be replaced with glob imports (core::*, alloc::*)

[fluiderson]

At first, I thought it'd be more convenient to maintain it this way if new modules would be added in core/alloc, but now I think it's easier to merge reimports than to try to exclude them from the common formatting rules.

@ark0f, glob imports create ambiguity because there are a lot of modules with the same name from core and alloc. Also I recreated some modules (e.g. collections), and they conflict with glob imports too.