feat: add prepare-input CLI

[hyperfinitism]

This PR adds a small CLI utility prepare-input to create the input JSON from SNP report (raw bin) and VCEK cert (PEM) used by the attestation flow.

What's changed

• Add /utils/prepare-input/*
• Update /Cargo.toml and /Cargo.lock
• Update /README.md

Usage

# short form
prepare-input -r report.bin -v vcek.pem -o input.json

# long form
prepare-input --report report.bin --vcek vcek.pem --out input.json

Test

Tested on Windows 11 (x86_64). This tool should also work on Linux/macOS with AArch64/x86_64.

# Build
git clone https://github.com/hyperfinitism/trustless-attestation-verification-risczero -b feature/prepare-input
cd trustless-attestation-verification-risczero
cargo build -r -p prepare-input

# Download sample input from main project repository
wget -O report.bin https://raw.githubusercontent.com/tiktok-privacy-innovation/trustless-attestation-verification/cb4f0eea5c4ec7fffaa2d0e1c1b557967a3a12cf/samples/report.bin
wget -O vcek.pem  https://raw.githubusercontent.com/tiktok-privacy-innovation/trustless-attestation-verification/cb4f0eea5c4ec7fffaa2d0e1c1b557967a3a12cf/samples/vcek.pem

# Run (Linux/macOS)
./target/release/prepare-input -r report.bin -v vcek.pem -o input.json

# Run (Windows)
./target/release/prepare-input.exe -r report.bin -v vcek.pem -o input.json