Support stats "yjit_alloc_size" (#3661)

What does this PR do?

Add stats "yjit_alloc_size"
which stats is available by default since Ruby 3.3
yjit_alloc_size and several more metadata-related stats are now available by default.
ref: ruby-lang.org/en/news/2023/12/25/ruby-3-3-0-released

Motivation:

The new metrics helps us tune --yjit-exec-mem-size option.
Monitoring both code_region_size and yjit_alloc_size makes it easier to understand the impact of YJIT's memory usage. (translated by DeepL)
ref: gihyo.jp/article/2024/01/ruby3.3-jit

* Support stats "yjit_alloc_size"

* Disable cop: Metrics/MethodLength

lib/datadog/core/runtime/metrics.rb:143:9: C: Metrics/MethodLength: Method has too many lines. [40/36]
        def flush_yjit_stats ...
        ^^^^^^^^^^^^^^^^^^^^

* Add Ruby 3.3 to matrix target in test-yjit

* Run test for metric :yjit_alloc_size if Ruby.version >= 3.3

ref: https://github.com/ruby/ruby/blob/029d92b8988d26955d0622f0cbb8ef3213200749/doc/NEWS/NEWS-3.3.0.md?plain=1#L435

---------

Co-authored-by: Oleg Pudeyev <code@olegp.name>

lib/datadog/core/environment/yjit.rb

@@ -47,6 +47,11 @@ def object_shape_count
           ::RubyVM::YJIT.runtime_stats[:object_shape_count]
         end
 
+        # Size of memory Rust allocated for metadata
+        def yjit_alloc_size
+          ::RubyVM::YJIT.runtime_stats[:yjit_alloc_size]
+        end
+
         def available?
           defined?(::RubyVM::YJIT) \
             && ::RubyVM::YJIT.enabled? \

lib/datadog/core/runtime/ext.rb

@@ -30,6 +30,7 @@ module Metrics
           METRIC_YJIT_LIVE_PAGE_COUNT = 'runtime.ruby.yjit.live_page_count'
           METRIC_YJIT_OBJECT_SHAPE_COUNT = 'runtime.ruby.yjit.object_shape_count'
           METRIC_YJIT_OUTLINED_CODE_SIZE = 'runtime.ruby.yjit.outlined_code_size'
+          METRIC_YJIT_YJIT_ALLOC_SIZE = 'runtime.ruby.yjit.yjit_alloc_size'
 
           TAG_SERVICE = 'service'
         end

lib/datadog/core/runtime/metrics.rb

@@ -140,6 +140,7 @@ def gauge_if_not_nil(metric_name, metric_value)
           gauge(metric_name, metric_value) if metric_value
         end
 
+        # rubocop:disable Metrics/MethodLength
         def flush_yjit_stats
           # Only on Ruby >= 3.2
           try_flush do
@@ -176,9 +177,14 @@ def flush_yjit_stats
                 Core::Runtime::Ext::Metrics::METRIC_YJIT_OUTLINED_CODE_SIZE,
                 Core::Environment::YJIT.outlined_code_size
               )
+              gauge_if_not_nil(
+                Core::Runtime::Ext::Metrics::METRIC_YJIT_YJIT_ALLOC_SIZE,
+                Core::Environment::YJIT.yjit_alloc_size
+              )
             end
           end
         end
+        # rubocop:enable Metrics/MethodLength
       end
     end
   end

sig/datadog/core/environment/yjit.rbs

@@ -10,6 +10,7 @@ module Datadog
         def self?.code_gc_count: () -> untyped
         def self?.code_region_size: () -> untyped
         def self?.object_shape_count: () -> untyped
+        def self?.yjit_alloc_size: () -> untyped
 
         def self?.available?: () -> untyped
       end

spec/datadog/core/runtime/metrics_spec.rb

@@ -240,6 +240,12 @@
             expect(runtime_metrics).to have_received(:gauge)
               .with(Datadog::Core::Runtime::Ext::Metrics::METRIC_YJIT_OUTLINED_CODE_SIZE, kind_of(Numeric))
               .once
+
+            if RUBY_VERSION >= '3.3.0'
+              expect(runtime_metrics).to have_received(:gauge)
+                .with(Datadog::Core::Runtime::Ext::Metrics::METRIC_YJIT_YJIT_ALLOC_SIZE, kind_of(Numeric))
+                .once
+            end
           end
         end
       end