Summary

Fixes #2218.

AsyncHttpClient reuses a single Bootstrap instance for every outbound
connection. On each connect, Netty's AbstractBootstrap.newOptionsArray()
copies the shared options map under synchronized (options):

synchronized (options) {
    return new ArrayList<Map.Entry<ChannelOption<?>, Object>>(options.entrySet())
            .toArray(EMPTY_OPTION_ARRAY);
}

Because the same Bootstrap (and its options map) backs every connection,
this is a single global monitor that all connection attempts contend on.
Under high connection-establishment rates — many concurrent outbound
requests, short-lived connections with low reuse, or no effective per-host
connection cap — threads queue on this lock and a convoy forms.

Fix

Stop configuring options on the Bootstrap. Instead:

• Resolve the configured ChannelOptions once at construction into a
  fixed array (buildChannelOptions). Conditional options (connect timeout,
  SO_LINGER, send/receive buffers) and all config getters are evaluated a
  single time rather than per connection.
• Apply that pre-resolved array to each channel from AHC's existing channel
  initializer via the public Channel.config().setOption(...) API
  (applyChannelOptions), leaving the Bootstrap options map empty.

This removes the global lock from the connect path entirely while preserving
identical behavior:

• Same option values and ordering — user-supplied options are still
  applied last so they override defaults, matching the previous Bootstrap
  order.
• Same timing — ChannelInitializer.initChannel runs during channel
  registration (handlerAdded, channel already registered), which is before
  the connect listener fires, so options are set before the channel connects.
  The connect-timeout option is honored because Netty reads it at connect time.
• The SOCKS proxy path is covered automatically, since it installs the HTTP
  channel initializer into its pipeline.

Scope is limited to ChannelManager.

Benefits

• Eliminates the lock convoy on the connect path.
• Avoids re-reading config and rebuilding the options array per connection
  (fewer per-connect allocations).
• No behavioral or configuration changes for users.