feat: speed up auth phase

[bdraco]

We now try to read a whole line at a time
since there is no risk of reading too far
ahead given that the spec says:

The first octet received by the server after the \r\n of the BEGIN command from the client must be the first octet of the authenticated/encrypted stream of D-Bus messages.

Unlike all other commands, the server does not reply to the BEGIN command with an authentication command of its own. After the \r\n of the reply to the command before BEGIN, the next octet received by the client must be the first octet of the authenticated/encrypted stream of D-Bus messages.

This avoids 26 read syscalls on average

fixes #128

[codecov]

Codecov Report

Base: 81.72% // Head: 81.66% // Decreases project coverage by -0.05% ⚠️

Coverage data is based on head (943ea01) compared to base (f8c67ed).
Patch coverage: 50.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #131      +/-   ##
==========================================
- Coverage   81.72%   81.66%   -0.06%     
==========================================
  Files          27       27              
  Lines        3091     3092       +1     
  Branches      597      597              
==========================================
- Hits         2526     2525       -1     
  Misses        347      347              
- Partials      218      220       +2     

Impacted Files	Coverage Δ
src/dbus_fast/__version__.py	0.00% <0.00%> (ø)
src/dbus_fast/_private/unmarshaller.py	95.29% <0.00%> (ø)
src/dbus_fast/_private/_cython_compat.py	100.00% <100.00%> (ø)
src/dbus_fast/aio/message_bus.py	85.98% <100.00%> (ø)
src/dbus_fast/message_bus.py	71.00% <0.00%> (-0.38%)	⬇️

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[bdraco]

60    getpid()                          = 60
60    sendto(56, "\0", 1, 0, NULL, 0)   = 1
60    getuid()                          = 0
60    sendto(56, "AUTH EXTERNAL 30\r\n", 18, 0, NULL, 0) = 18
60    recvfrom(56, "OK 27ecd1c33de69bca61bcaf91be376fc6\r\n", 1024, 0, NULL, NULL) = 37
60    sendto(56, "NEGOTIATE_UNIX_FD\r\n", 19, 0, NULL, 0) = 19
60    recvfrom(56, "AGREE_UNIX_FD\r\n", 1024, 0, NULL, NULL) = 15
60    sendto(56, "BEGIN\r\n", 7, 0, NULL, 0) = 7
60    epoll_ctl(4, EPOLL_CTL_ADD, 56, {events=EPOLLIN, data={u32=56, u64=281470681743416}}) = 0
60    sendto(56, "l\1\0\1\0\0\0\0\1\0\0\0m\0\0\0\1\1o\0\25\0\0\0/org/freedesktop/DBus\0\0\0\2\1s\0\24\0\0\0org.freedesktop.DBus\0\0\0\0\3\1s\0\5\0\0\0Hello\0\0\0\6\1s\0\24\0\0\0org.freedesktop.DBus\0\0\0\0", 128, 0, NULL, 0) = 128

Looks much better now