Fix #2612: adjust readable trait to allow try_peek (#2714)

* Fix #2612: adjust readable trait to allow try_peek

Our implementation for Readable was inconsistent.
We had a try_unchecked variant for read but not for peek.
This resolves that by making a breaking change to the
Readable interface.

* fix doctests too

Cargo.lock

@@ -10382,7 +10382,7 @@ source = "git+https://github.com/DioxusLabs/warnings#9889b96cccb6ac91a8af924cfee
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.71",
+ "syn 2.0.72",
 ]
 
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