Support for no_std

[Person-93]

We've started talking about no_std in a few different PRs and issues, so I thouhght I'd start a discussion to keep the plan in one place.

• Add the clippy lints for using std instead of core/alloc and alloc instead of core. Do the mechanical transformations to satisfy those lints.
  • In ffi crate
  • In main crate - internal: use std as extern crate #6054
• Make the ffi crate no_std for python versions 3.14 and up (possibly older than that as well for wasm builds).
• Add an std feature to the main crate and choose suitable replacements for anything currently using std.
  • Replace/remove usage of eprintln internal: use std as extern crate #6054 (comment)
• Testing
  • Enable as much of the test suite as possible for wasm builds
  • Include no_std testing in the nox file
• Add section to the contributing guide explaining the common patterns for dealing with CI breakage
• Fully document behavior differences
  • Panics in pymethods will abort at FFI boundary instead of throwing a PanicException

Previous discussions:

• Make the ffi crate no_std #6022
• No std #5856
• MicroPython + PyO3 + #![no_std] - call for participation #3510