One of the biggest remaining contention point is `RClass.cc_table`.
The logical solution would be to turn it into a managed object, so
we can use an RCU strategy, given it's read heavy.

However, that's not currently possible because the table can't
be freed before the owning class, given the class free function
MUST go over all the CC entries to invalidate them.

However if the `CC->klass` reference is weak marked, then the
GC will take care of setting the reference to `Qundef`.

It has been marked as obsolete for a while and I see no reason
to keep it.

This behave almost exactly as a T_OBJECT, the layout is entirely
compatible.

This aims to solve two problems.

First, it solves the problem of namspaced classes having
a single `shape_id`. Now each namespaced classext
has an object that can hold the namespace specific
shape.

Second, it open the door to later make class instance variable
writes atomics, hence be able to read class variables
without locking the VM.
In the future, in multi-ractor mode, we can do the write
on a copy of the `fields_obj` and then atomically swap it.

Considerations:

  - Right now the `RClass` shape_id is always synchronized,
    but with namespace we should likely mark classes that have
    multiple namespace with a specific shape flag.

This commit inlines instructions for Class#new.  To make this work, we
added a new YARV instructions, `opt_new`.  `opt_new` checks whether or
not the `new` method is the default allocator method.  If it is, it
allocates the object, and pushes the instance on the stack.  If not, the
instruction jumps to the "slow path" method call instructions.

Old instructions:

```
> ruby --dump=insns -e'Object.new'
== disasm: #<ISeq:<main>@-e:1 (1,0)-(1,10)>
0000 opt_getconstant_path                   <ic:0 Object>             (   1)[Li]
0002 opt_send_without_block                 <calldata!mid:new, argc:0, ARGS_SIMPLE>
0004 leave
```

New instructions:

```
> ./miniruby --dump=insns -e'Object.new'
== disasm: #<ISeq:<main>@-e:1 (1,0)-(1,10)>
0000 opt_getconstant_path                   <ic:0 Object>             (   1)[Li]
0002 putnil
0003 swap
0004 opt_new                                <calldata!mid:new, argc:0, ARGS_SIMPLE>, 11
0007 opt_send_without_block                 <calldata!mid:initialize, argc:0, FCALL|ARGS_SIMPLE>
0009 jump                                   14
0011 opt_send_without_block                 <calldata!mid:new, argc:0, ARGS_SIMPLE>
0013 swap
0014 pop
0015 leave
```

This commit speeds up basic object allocation (`Foo.new`) by 60%, but
classes that take keyword parameters see an even bigger benefit because
no hash is allocated when instantiating the object (3x to 6x faster).

Here is an example that uses `Hash.new(capacity: 0)`:

```
> hyperfine "ruby --disable-gems -e'i = 0; while i < 10_000_000; Hash.new(capacity: 0); i += 1; end'" "./ruby --disable-gems -e'i = 0; while i < 10_000_000; Hash.new(capacity: 0); i += 1; end'"
Benchmark 1: ruby --disable-gems -e'i = 0; while i < 10_000_000; Hash.new(capacity: 0); i += 1; end'
  Time (mean ± σ):      1.082 s ±  0.004 s    [User: 1.074 s, System: 0.008 s]
  Range (min … max):    1.076 s …  1.088 s    10 runs

Benchmark 2: ./ruby --disable-gems -e'i = 0; while i < 10_000_000; Hash.new(capacity: 0); i += 1; end'
  Time (mean ± σ):     627.9 ms ±   3.5 ms    [User: 622.7 ms, System: 4.8 ms]
  Range (min … max):   622.7 ms … 633.2 ms    10 runs

Summary
  ./ruby --disable-gems -e'i = 0; while i < 10_000_000; Hash.new(capacity: 0); i += 1; end' ran
    1.72 ± 0.01 times faster than ruby --disable-gems -e'i = 0; while i < 10_000_000; Hash.new(capacity: 0); i += 1; end'
```

This commit changes the backtrace for `initialize`:

```
aaron@tc ~/g/ruby (inline-new)> cat test.rb
class Foo
  def initialize
    puts caller
  end
end

def hello
  Foo.new
end

hello
aaron@tc ~/g/ruby (inline-new)> ruby -v test.rb
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [arm64-darwin24]
test.rb:8:in 'Class#new'
test.rb:8:in 'Object#hello'
test.rb:11:in '<main>'
aaron@tc ~/g/ruby (inline-new)> ./miniruby -v test.rb
ruby 3.5.0dev (2025-03-28T23:59:40Z inline-new c4157884e4) +PRISM [arm64-darwin24]
test.rb:8:in 'Object#hello'
test.rb:11:in '<main>'
```

It also increases memory usage for calls to `new` by 122 bytes:

```
aaron@tc ~/g/ruby (inline-new)> cat test.rb
require "objspace"

class Foo
  def initialize
    puts caller
  end
end

def hello
  Foo.new
end

puts ObjectSpace.memsize_of(RubyVM::InstructionSequence.of(method(:hello)))
aaron@tc ~/g/ruby (inline-new)> make runruby
RUBY_ON_BUG='gdb -x ./.gdbinit -p' ./miniruby -I./lib -I. -I.ext/common  ./tool/runruby.rb --extout=.ext  -- --disable-gems  ./test.rb
656
aaron@tc ~/g/ruby (inline-new)> ruby -v test.rb
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [arm64-darwin24]
544
```

Thanks to @ko1 for coming up with this idea!

Co-Authored-By: John Hawthorn <john@hawthorn.email>

Add missing counters to rb_debug_counter_type enum

On master we have calls to the RB_DEBUG_COUNTER_INC macro
for counters that are not getting defined in the
rb_debug_counter_type enum.

This commit adds those that are missing in order for
compilation to pass with -DUSE_RUBY_DEBUG_LOG.