MVP no_std for wgpu-core

[bushrat011899]

Connections

• Contributes to Support no_std where possible (specifically for wasm32v1-none) #6826

Description

Adds no_std support to wgpu-core through 3 changes:

1. Use num-traits within timestamp_normalization to account for the floating point methods only available with std.
2. Make parking_lot optional by falling back to either std::sync::{Mutex, RwLock}, spin::{Mutex, RwLock}, or core::cell::RefCell based on selecting either parking_lot, std, spin, or no locking implementation.
   a. Note that spin was already in the lockfile via crossbeam-deque so this feature is "free"
   b. Note that RefCell is !Sync, so users should select spin in no_std environments. The use of RefCell as a fallback just allows compilation to succeed without any features enabled.
3. Make once_cell optional by falling back to core::cell:OnceCell.
   a. Note that once_cell is no_std compatible, but it requires activating the critical-section feature to access its implementation of OnceCell. Adding such a feature would therefore add critical-section to the lockfile, requiring thorough review due to its use of unsafe and extern "Rust". I believe it is a safe inclusion, but it can be avoided here so I'd rather save that quality of life feature for a follow-up. Users are still able to use once_cell with wgpu-core on no_std, they just have to enable once_cell/critical-section themselves.
   b. Note that core::cell::OnceCell is !Sync, so users should prefer to enable critical-section themselves.

To preserve existing behavior, the newly added parking_lot and once_cell features are enabled by default.

Testing

Added wgpu-core to the wasm32v1-none CI test.

Squash or Rebase?

Squash

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.