Previously, we allocated a 512-byte buffer for every call of the
formatted panic function. This was heavily increasing the stack size for
a number of functions.

We now don't print to a statically allocated buffer, but rather use the
iterator-based formatting facility and a proxy iterator with a small,
self-flushing buffer. This reduces that static overhead of the formatted
panic function to by almost 500 bytes, while increasing possible message
fidelity, since we are not longer arbitrarily limited by the buffer.