Replace byebug with the debug gem included in Ruby

Byebug hasn't been maintained for years, and it isn't fully compatible
with Zeitwerk [1]. On the other hand, Ruby includes the debug gem since
version 3.1.0. We tried to start using at after commit e74eff217, but
couldn't do so because our CI was hanging forever in a test related to
machine learning, with the message:

> DEBUGGER: Attaching after process X fork to child process Y

(Note this message appeared with debug 1.6.3 but not with the version
we're currently using.)

So we're changing the debug gem fork mode in the test so it doesn't hang
anymore when running our CI. We tried to change the test so it wouldn't
call `Process.fork`, but this required changing the code, and since
there are no tests checking machine learning behavior with real scripts,
we aren't sure whether these script would keep working after changing
the code.

[1] Issue 564 in https://github.com/deivid-rodriguez/byebug

Gemfile.lock

@@ -106,7 +106,6 @@ GEM
     bullet (7.1.6)
       activesupport (>= 3.0.0)
       uniform_notifier (~> 1.11)
-    byebug (11.1.3)
     cancancan (3.5.0)
     capistrano (3.18.1)
       airbrussh (>= 1.0.0)
@@ -171,6 +170,9 @@ GEM
     daemons (1.4.1)
     dalli (3.2.8)
     date (3.3.4)
+    debug (1.9.2)
+      irb (~> 1.10)
+      reline (>= 0.3.8)
     delayed_job (4.1.11)
       activesupport (>= 3.0, < 8.0)
     delayed_job_active_record (4.1.8)
@@ -282,6 +284,10 @@ GEM
       ruby-vips (>= 2.0.17, < 3)
     invisible_captcha (2.3.0)
       rails (>= 5.2)
+    io-console (0.7.2)
+    irb (1.12.0)
+      rdoc
+      reline (>= 0.4.2)
     json (2.7.1)
     jwt (2.7.1)
     kaminari (1.2.2)
@@ -438,6 +444,8 @@ GEM
     pronto-stylelint (0.10.3)
       pronto (>= 0.10, < 0.12)
       rugged (>= 0.24, < 2.0)
+    psych (5.1.2)
+      stringio
     public_suffix (4.0.7)
     puma (5.6.8)
       nio4r (~> 2.0)
@@ -486,10 +494,14 @@ GEM
     rainbow (3.1.1)
     rake (13.1.0)
     rbtree3 (0.7.1)
+    rdoc (6.6.3.1)
+      psych (>= 4.0.0)
     recipient_interceptor (0.3.1)
       mail
     redcarpet (3.6.0)
     regexp_parser (2.9.0)
+    reline (0.5.1)
+      io-console (~> 0.5)
     request_store (1.6.0)
       rack (>= 1.4)
     responders (3.1.1)
@@ -615,6 +627,7 @@ GEM
       net-scp (>= 1.1.2)
       net-sftp (>= 2.1.2)
       net-ssh (>= 2.8.0)
+    stringio (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     terrapin (0.6.0)
@@ -683,7 +696,6 @@ DEPENDENCIES
   autoprefixer-rails (~> 10.4.16)
   bing_translator (~> 6.2.0)
   bullet (~> 7.1.6)
-  byebug (~> 11.1.3)
   cancancan (~> 3.5.0)
   capistrano (~> 3.18.1)
   capistrano-bundler (~> 2.1.0)
@@ -699,6 +711,7 @@ DEPENDENCIES
   cocoon (~> 1.2.15)
   daemons (~> 1.4.1)
   dalli (~> 3.2.8)
+  debug (~> 1.9.2)
   delayed_job_active_record (~> 4.1.8)
   devise (~> 4.9.3)
   devise-security (~> 0.18.0)