proc.c: Make Method and UnboundMethod embded

Avoid some needless malloc churn

```
compare-ruby: ruby 3.3.0dev (2023-11-20T02:02:55Z master 701b0650de) [arm64-darwin22]
last_commit=[ruby/prism] feat: add encoding for IBM865 (https://github.com/ruby/prism/pull/1884)
built-ruby: ruby 3.3.0dev (2023-11-20T16:23:07Z embedded-methods e35284bfaa) [arm64-darwin22]
warming up..

|                         |compare-ruby|built-ruby|
|:------------------------|-----------:|---------:|
|allocate_method          |      8.413M|   12.333M|
|                         |           -|     1.47x|
|allocate_unbound_method  |      8.083M|   11.607M|
|                         |           -|     1.44x|
```

```
prelude: |
  class SomeClass
    def foo
    end
  end
  some_object = SomeClass.new
benchmark:
  allocate_method: some_object.method(:foo)
  allocate_unbound_method: SomeClass.instance_method(:foo)
```

0 files changed, 0 insertions, 0 deletions