Introduce a specialize instruction for Array#pack

Instructions for this code:

```ruby
  # frozen_string_literal: true

[a].pack("C")
```

Before this commit:

```
== disasm: #<ISeq:<main>@test.rb:1 (1,0)-(3,13)>
0000 putself                                                          (   3)[Li]
0001 opt_send_without_block                 <calldata!mid:a, argc:0, FCALL|VCALL|ARGS_SIMPLE>
0003 newarray                               1
0005 putobject                              "C"
0007 opt_send_without_block                 <calldata!mid:pack, argc:1, ARGS_SIMPLE>
0009 leave
```

After this commit:

```
== disasm: #<ISeq:<main>@test.rb:1 (1,0)-(3,13)>
0000 putself                                                          (   3)[Li]
0001 opt_send_without_block                 <calldata!mid:a, argc:0, FCALL|VCALL|ARGS_SIMPLE>
0003 putobject                              "C"
0005 opt_newarray_send                      2, :pack
0008 leave
```

Co-authored-by: Maxime Chevalier-Boisvert <[email protected]>
Co-authored-by: Aaron Patterson <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/pack.c b/pack.c
index 4fdaf7fd89..1b0d66f990 100644
--- a/pack.c
+++ b/pack.c
@@ -782,6 +782,12 @@ pack_pack(rb_execution_context_t *ec, VALUE ary, VALUE fmt, VALUE buffer)
     return res;
 }
 
+VALUE
+rb_ec_pack_ary(rb_execution_context_t *ec, VALUE ary, VALUE fmt, VALUE buffer)
+{
+    return pack_pack(ec, ary, fmt, buffer);
+}
+
 static const char uu_table[] =
 "`!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_";
 static const char b64_table[] =