Add support for smol_str::SmolStr

[AndreyErmilov]

Hi, thank you for the crate!
This PR adds Encode/Decode support for smol_str::SmolStr behind an optional smol_str feature flag, following the same pattern as the existing uuid, time, and rust_decimal integrations.

[finnbear]

Hello, thanks for the PR!

For efficiency, bitcode checks UTF-8 of multiple strings at once during decoding and vectorizes during encoding. However, this requires using a more specialized pattern than DerefEncoder and FromDecoder. The following snippets can be adapted for SmolStr. Please make an impl_string macro that can be used to support anything with the API of String, and use it for String and SmolStr. You will have to use <T>::from(&str) instead of <str>::to_owned(&self).

• Encode:

  bitcode/src/str.rs

  Lines 60 to 73 in d0049d9

  	impl Encoder<String> for StrEncoder {
  	#[inline(always)]
  	fn encode(&mut self, t: &String) {
  	self.encode(t.as_str());
  	}
  	#[inline(always)]
  	fn encode_vectored<'a>(&mut self, i: impl Iterator<Item = &'a String> + Clone)
  	where
  	String: 'a,
  	{
  	self.encode_vectored(i.map(String::as_str));
  	}
  	}

• Decode:

  bitcode/src/str.rs

  Lines 134 to 140 in d0049d9

  	impl<'a> Decoder<'a, String> for StrDecoder<'a> {
  	#[inline(always)]
  	fn decode(&mut self) -> String {
  	let v: &str = self.decode();
  	v.to_owned()
  	}
  	}

Secondly, please enable SmolStr's serde support so the fuzzer passes.

[AndreyErmilov]

Hi, @finnbear! Thank you for the comments.
Could you please check out the update? I hope I understood everything correctly.
I've encountered a problem with MSRV - smol_str 0.3.4+ uses edition 2024 and requires Rust 1.89, while bitcode's MSRV is 1.70. The only non-yanked version compatible with 1.70 is 0.3.2. Pinning to a single old version isn't a great solution. Do you have any plans to bump the MSRV to 1.89 or higher? Asking just in case :)

[finnbear]

Thanks, looks good. Next time I work on bitcode (could be weeks/months from now), I'll fully review and likely merge this, making any remaining edits myself.

Regarding MSRV, this seems like a non-issue because:

• it's an optional dependency
• we can say version="0.3.2" which is not the same as pinning (version="=0.3.2"), and is fully compatible with "0.3.4+"