fix: do not wrap io.EOF in errd.Wrap

[Yanhu007]

Fixes #561

Problem

The errd.Wrap helper wraps all non-nil errors using fmt.Errorf("%w"). When io.EOF is returned (e.g. from Conn.reader), it becomes "failed to get reader: EOF". Per Go convention, io.EOF must never be wrapped:

EOF is the error returned by Read when no more input is available.
(Read must return EOF itself, not an error wrapping EOF,
because callers will test for EOF using ==.)

This breaks callers like io.Copy and bufio.Scanner that test err == io.EOF.

Fix

Skip wrapping in errd.Wrap when the error is exactly io.EOF:

func Wrap(err *error, f string, v ...any) {
    if *err != nil && *err != io.EOF {
        *err = fmt.Errorf(f+": %w", append(v, *err)...)
    }
}