Log loaded extensions behind `PUMA_DEBUG`

[Patrik Ragnarsson]

Re the 'loaded extensions', maybe something like the below?

Single mode:

* Listening on http://127.0.0.1:40001
* Loaded Extensions:
*     /mnt/c/GitHub/puma/vendor/bundle/ubuntu22/ruby/3.2.0+1/gems/nio4r-2.5.8/lib/nio4r_ext.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/date_core.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/enc/encdb.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/enc/trans/transdb.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/etc.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/io/wait.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/monitor.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/pathname.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/socket.so
*     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/stringio.so
Use Ctrl-C to stop

Cluster mode:

[16449] * Listening on http://127.0.0.1:40001
[16449] * Loaded Extensions:
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/date_core.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/enc/encdb.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/enc/trans/transdb.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/etc.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/io/wait.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/monitor.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/pathname.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/socket.so
[16449] *     /usr/local/lib/ruby/3.2.0+1/x86_64-linux/stringio.so
[16449] Use Ctrl-C to stop

EDIT: Above were generated without io-wait in Gemfile.lock

Originally posted by @MSP-Greg in #2843 (comment)

[MSP-Greg]

JFYI, this week I did briefly look for the code that generated this; I couldn't find it. I'll look more this weekend, otherwise may rewrite. Regardless, anyone else can contribute.