Use mini-alloc by default and remove panic handler (#373)

Mi intention is not that we directly merge this PR, but that it serves 2
purposes
1. Discuss how we want to handle global allocator and mainly what to do
about the panic handler
2. In case we proceed wether we want to merge it to the release
branch(and issue a new release) or just to main

## Background
While testing how the experience will be for someone that creates a new
stylus project by running `cargo stylus new` I realized a couple things
that I think hurt DX.
1. You have to disable the default feature flags on the stylus sdk(which
disables mini_alloc as the default globall allocator). Otherwise you get
#global_allocator conflicts as it is defined in two places(the stylus
sdk and our library).
``` toml
stylus-sdk = { version = "=0.6.0", default-features = false }
```
2. Since our library is `#[no_std]` by default it defines a custom
panic_handler such that if you use it from a `no_std `environment you
don’t have to define it yourself. The problem is that if you want to use
the std library in your project(and that seems to be a reasonable
assumption according to
[this](https://github.com/OffchainLabs/stylus-sdk-rs/tree/main?tab=readme-ov-file#feature-highlights)),
you cannot do it since it results in a duplication of the panic_handler
function. This is also the default behavior when you create a new
project with `cargo stylus new`.

## Proposed Solution
1. Using mini-alloc by default via the sdk seems like the best approach
as it was one of the recommendations from the
[audit](https://forum.arbitrum.foundation/t/stylus-sdk-audit/26674#p-58099-inefficient-allocator-fallback-in-stylus-contracts-44)
and is what is used when creating a new project via `cargo stylus new`.
2. Here I see two options:
- Add a compilation flag to the panic handler such that it is not
included if built with std flag on. This is the approach I took in this
PR, but it has 2 downsides:
1. If you just start a project from scratch using `cargo stylus new` it
is harder to realize and you might spend some time trying to figure it
out.
2. We are now encouraging people to use the `std` flag on our library,
which might enable other behaviors we haven’t considered? Since we’ve
been mainly using it for testing
- Remove the panic handler entirely from the library, allowing projects
building with std to have it included by default and projects explicitly
opting in to `no_std` and having zero dependencies on the std library
would have to define it themselves.
This approach is more reasonable IMO, since it makes it easier for
newcomers, but it requires some extra effort if you are experienced
enough to define your contracts with `no_std` .
The problem today is that we set the library type to
[cdylib](https://doc.rust-lang.org/reference/linkage.html), which
requires the crate to define a panic_handler when using `no_std` (more
info
[here](https://internals.rust-lang.org/t/panic-handler-free-no-std-targets/14697)).
If we find a way to do this, maybe this is the best approach, maybe it
is possible using unstable features.

## Edit
- We were able to remove the panic handler entirely by not targeting
`cdylib`(thanks @qalisander )! Now the user of the library can just use
`std`or define their own panic handler.
- [x] Test on a new stylus project
- [x] Update the Readme  
- [x] Update Changelog

---------

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

Author: 3 people

CHANGELOG.md

@@ -0,0 +1,31 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+-
+
+### Changed
+
+-
+
+### Fixed
+
+-
+
+## [0.1.1] - 2024-10-
+
+### Changed
+
+- Mini alloc is now used by default via the stylus-sdk. This avoids conflicts with duplicate #[global_allocator] definitions. #373
+- Removed the panic handler from the library, making it easier for `std` and `no_std` projects to use the library. #373
+
+## [0.1.0] - 2024-10-17
+
+- Initial release