v0.18.10 : update alloy to 0.3.1

Updated alloy to 0.3.1. This warrants a release because of this change, which smithy4s leverages to let @nullable hints through when compiling interpreters, which impacts serialisation.

Without this upgrade, the SimpleRestJsonBuilder doesn't know that nullable should be taken into consideration, and filters the corresponding hints out before compiling the schema into json codecs.

What's Changed

• Update scala-library, scala-reflect to 2.12.19 by @scala-steward in #1420
• Update alloy to 0.3.1 by @Baccata in #1423

Full Changelog: v0.18.9...v0.18.10