Ensure that lox_library::bridge_table::BRIDGE_BYTES is large enough

The constant BRIDGE_BYTES is current set to 250. While tor bridge lines are currently (in c-tor) capped at 510 bytes, the Lox bridge line format does not match the tor bridge line format, so bridges that are well below the c-tor limit are causing panics in the lox distributor's parse_into_bridgelines function.

This is an opportunity to reconsider the Lox bridge line format and whether it can be improved, since the current format requires extra work for the client to turn it into a usable torrc bridge line string.