Add lambda_runtime: Mojo AWS Lambda custom runtime

[fourlexboehm]

Summary

Adds a lambda_runtime recipe for a Mojo AWS Lambda custom runtime library.

• Source: https://github.com/fourlexboehm/mojo-lambda-runtime @ fb83b01
• Library: lambda_runtime (.mojopkg) implementing the Lambda Runtime API over plain HTTP (libc sockets, no libcurl)
• Scaffold: installs share/lambda_runtime/ templates + lambda-runtime-init so users get Dockerfile / build.sh / deploy.sh without cloning the repo
• Deps: mojo-compiler =1.0.0b1, emberjson

Consumer flow

pixi add lambda_runtime \
  -c https://repo.prefix.dev/modular-community \
  -c https://conda.modular.com/max \
  -c conda-forge
lambda-runtime-init
# edit main.mojo
./build.sh   # provided.al2023 / arm64 zip

Test plan

• Request OK to test label so CI builds the recipe
• CI builds on linux-64 / linux-aarch64 / osx-arm64
• Package installs lib/mojo/lambda_runtime.mojopkg, share/lambda_runtime/*, bin/lambda-runtime-init
• After merge: pixi add lambda_runtime and run lambda-runtime-init --list

[fourlexboehm]

Updated the recipe to reviewed source commit 677d722ac20976a9c64552cbbef70163f9ddb45d. The recipe builds and all package tests pass locally on osx-arm64. I also built the generated arm64 consumer scaffold from the packaged .mojopkg, deployed it to AWS Lambda (provided.al2023), and successfully invoked it with response {"ok":true,"echo_chars":24}. Please add the OK to test label when ready.