Dependency on loom is circular

[adamgreig]

(cc @datdenkikniet )

Loom depends on tracing -> tracing-core -> once_cell -> critical_section, which means we end up with a circular dependency which Cargo refuses to resolve. I also thought the loom dependency was in some sense optional, but it seems like it gets enabled for all builds, so with the 1.3 release every project using critical-section fails to build! We've yanked the release for now, but it's not clear how to fix this if this crate can't have a dependency on loom.

[Dirbaio]

example of the dependency cycle:

cyclic package dependency: package `critical-section v1.3.0` depends on itself. Cycle:
package `critical-section v1.3.0`
    ... which satisfies dependency `critical-section = "^1.1.3"` of package `once_cell v1.21.4`
    ... which satisfies dependency `once_cell = "^1.13.0"` of package `tracing-core v0.1.36`
    ... which satisfies dependency `tracing-core = "^0.1.36"` of package `tracing v0.1.44`
    ... which satisfies dependency `tracing = "^0.1.27"` of package `loom v0.7.2`
    ... which satisfies dependency `loom = "^0.7.2"` of package `critical-section v1.3.0`
    ... which satisfies dependency `critical-section = "^1.0.0"` of package `cortex-m v0.7.7`
    ... which satisfies dependency `cortex-m = "^0.7"` of package `blinky-async v0.1.0 (/home/dirbaio/embassy/embassy/docs/examples/layer-by-layer/blinky-async)`