Revise 512 byte limit

[reynir]

We sometimes produce errors that are longer than 512 bytes for example this one when passing --dns_servers=172.23.0.53:

console 2025-11-05T12:55:24-00:00: Fatal error: exception Invalid_argument("Unable to decode nameserver 172.23.0.53\nThe format of an IP address and optional port is:\n- '[::1]:port' for an IPv6 address, or\n- '127.0.0.1:port' for an IPv4 address.\n\nThe format of a nameserver is:\n- 'udp:IP' where the first element is the string \"udp\" and the [IP] as described\n  above (port defaults to 53): UDP packets to the provided IP address will be\n  sent from a random source port;\n- 'tcp:IP' where the first element is the string \"tcp\" and the [ [truncated]

[hannesm]

What is a good limit then? Or should we shorten the error message instead?

[reynir]

The error message would work if it was printed and not escaped and packaged into a Invalid_argument. So we could consider that. I think this is a pattern we've used several places so it would be some work to find and adjust all the places.

FWIW logs-syslog.mirage uses truncate 65535 https://github.com/hannesm/logs-syslog/blob/ad0579ffcbde9a8569f551c8c6ff0d8c45afc145/src/mirage/logs_syslog_mirage.ml#L6