Output a warning if the input file is too large

[matiaskorhonen]

Adds a warning if the input file is too large. Only a warning though as the maximum size is slightly non-deterministic (but always around ~1952 bytes or so).

Crude test script to iterate through incrementally large inputs:

#!/bin/bash

counter=976

echo "Start $counter ($((counter * 2)) bytes)"

export PAPERAGE_PASSPHRASE="snakeoil"

while openssl rand -hex $counter | cargo run -- -f -;
do
  counter=$((counter + 1))
  echo "Loop $counter ($((counter * 2)) bytes)"
done

Will close #11.

[github-actions[bot]]

Package	Line Rate	Health
src/builder.rs	96%	✔
src/cli.rs	81%	✔
src/main.rs	88%	✔
tests/cli.rs	100%	✔
src/encryption.rs	100%	✔
src/builder/svg.rs	100%	✔
Summary	94% (502 / 533)	✔