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 d2930f8) +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 d2930f8) +PRISM [arm64-darwin24]
544
```

Thanks to @ko1 for coming up with this idea!

Co-Authored-By: John Hawthorn <[email protected]>