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• I've searched the issue tracker for similar requests

Is your feature request related to a problem? Please describe.

Now that rustls supports no-std, as discussed in issue #157, it would be nice if the CI testing could cover build & test with no-std on more and more embedded target CPUs & platforms, using cross to test in QEMU, for example:

• STM32, as discussed in: https://docs.rust-embedded.org/book/start/hardware.html
• Certain ESP32 microcontrollers coming with no support for atomics, as discussed in no-std support for targets w/o atomics? #2068

As a first step, I have contributed a proposal in #2095 to test with a limited number of emulated targets.

Describe the solution you'd like

Update CI to test on some more Tier 1 & Tier 2 platforms discussed here: https://doc.rust-lang.org/nightly/rustc/platform-support.html

Should be able to cover embedded CPUs such as STM32 & ESP32.

Should also cover build & test with --release option.

Describe alternatives you've considered

• use humans to do this testing - 👎
• use AI to do this testing - seems to be increasingly common these days

Additional context

N/A

One issue I discovered is that cargo test (and I think cross test) would always enable the std feature. So it would probably be best to include build test with no-std.

I would love to start working on these updates, assuming I can spare some time for this (someday).