Use TracePoint.allow_reentry when available

This fixes compatibility with TracePoint users such as Zeitwerk

Test script:

```ruby
require 'fileutils'
FileUtils.mkdir_p('/tmp/lib/foo')
File.write('/tmp/lib/foo.rb', 'module Foo; end')
File.write('/tmp/lib/foo/bar.rb', 'Foo::Bar = 1')

require 'zeitwerk'

loader = Zeitwerk::Loader.new
loader.push_dir('/tmp/lib')
loader.setup

require 'debug'
binding.break
p Foo::Bar
```

before:
```
[8, 16] in /tmp/debug-zeitwerk.rb
     8| loader = Zeitwerk::Loader.new
     9| loader.push_dir('/tmp/lib')
    10| loader.setup
    11|
    12| require 'debug'
=>  13| binding.break
    14| p Foo::Bar
    15|
    16| p :done
=>#0    <main> at /tmp/debug-zeitwerk.rb:13
(rdbg) p Foo::Bar    # command
eval error: uninitialized constant Foo::Bar
  (rdbg)//tmp/debug-zeitwerk.rb:1:in `<main>'
=> nil
```

after:
```
[8, 16] in /tmp/debug-zeitwerk.rb
     8| loader = Zeitwerk::Loader.new
     9| loader.push_dir('/tmp/lib')
    10| loader.setup
    11|
    12| require 'debug'
=>  13| binding.break
    14| p Foo::Bar
    15|
    16| p :done
=>#0    <main> at /tmp/debug-zeitwerk.rb:13
(rdbg) p Foo::Bar    # command
=> 1
```

Author: byroot

lib/debug/thread_client.rb

@@ -367,7 +367,11 @@ def frame_eval src, re_raise: false
 
       result = if b
                   f, _l = b.source_location
-                  b.eval(src, "(rdbg)/#{f}")
+                  if TracePoint.respond_to?(:allow_reentry)
+                    TracePoint.allow_reentry { b.eval(src, "(rdbg)/#{f}") }
+                  else
+                    b.eval(src, "(rdbg)/#{f}")
+                  end
                 else
                   frame_self = current_frame.self
                   instance_eval_for_cmethod(frame_self, src)
@@ -406,9 +410,9 @@ def show_src(frame_index: @current_frame_index,
           unless start_line
             if frame.show_line
               if dir > 0
-                start_line = frame.show_line
+                start_line = frame.show_line.lineno
               else
-                end_line = frame.show_line - max_lines
+                end_line = frame.show_line.lineno - max_lines
                 start_line = [end_line - max_lines, 0].max
               end
             else