test: Investigate Fuzzing (#477)

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As [per our
agreement](https://openzeppelin.slack.com/archives/C06R5AGFE9G/p1737021738986409),
this PR includes a basic fuzz tests setup and some missing unit/property
tests for `openzeppelin-crypto` crate.

I created a couple of related issues to address missing property tests
(see #501 #502 #503).
Adding property tests for contract will be easily possible after `motsu`
is refactored (see
https://github.com/OpenZeppelin/stylus-test-helpers/pull/14/files#r1919897820)

<!-- Fill in with issue number -->
Resolves #458 

#### PR Checklist

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- [x] Tests
- [x] Documentation
- [ ] Changelog

---------

Co-authored-by: Daniel Bigos <[email protected]>
Co-authored-by: Alisander Qoshqosh <[email protected]>

Cargo.toml

@@ -52,6 +52,7 @@ default-members = [
   "examples/ecdsa",
   "examples/poseidon",
 ]
+exclude = ["fuzz"]
 
 # Explicitly set the resolver to version 2, which is the default for packages
 # with edition >= 2021.

GUIDELINES.md

@@ -212,19 +212,25 @@ Some other examples of automation are:
 
 Always check your code with the linter (`clippy`), by running:
 
-    $ cargo clippy --tests --all-features
+```shell
+    cargo clippy --tests --all-features
+```
 
 And make sure your code is formatted with, using:
 
-    $ cargo +nightly fmt
+```shell
+    cargo +nightly fmt
+```
 
 Finally, ensure there is no trailing whitespace anywhere.
 
 ### Running tests
 
 Make sure all tests are passing with:
 
-    $ cargo test --all-features
+```shell
+    cargo test --all-features
+```
 
 ### Running end-to-end tests
 
@@ -241,12 +247,31 @@ Then you will be able to run e2e tests:
 ./scripts/e2e-tests.sh
 ```
 
+### Running fuzz tests
+
+To run fuzz tests, you need to have [cargo-fuzz] installed. 
+Then from the root of the project you can use `cargo fuzz list` to view the list of all existing fuzz targets:
+
+```shell
+    cargo fuzz list
+```
+
+Finally you need to run:
+
+```shell
+    cargo fuzz run <fuzz target name>
+```
+
+[cargo-fuzz]: https://rust-fuzz.github.io/book/cargo-fuzz/setup.html
+
 ### Checking the docs
 
 If you make documentation changes, you may want to check whether there are any
 warnings or errors:
 
-    $ cargo doc --all-features
+```shell
+    cargo doc --all-features
+```
 
 ## Pull requests
 

fuzz/.gitignore

@@ -0,0 +1,4 @@
+target
+corpus
+artifacts
+coverage