Enable type checking for AgentSettingsResolver/AgentSettings

Steep doesn't seem to be a big fan of Structs so I just went ahead
and turned the `AgentSettings` into a regular class that's equivalent
to the struct we had before.

(In particular, I decided to still keep every field as optional).

Ideally this would be a `Data` class, but we're far from dropping
support for Rubies that don't have it.

Steepfile

@@ -80,7 +80,6 @@ target :datadog do
   ignore 'lib/datadog/core/buffer/thread_safe.rb'
   ignore 'lib/datadog/core/chunker.rb'
   ignore 'lib/datadog/core/configuration.rb'
-  ignore 'lib/datadog/core/configuration/agent_settings_resolver.rb'
   ignore 'lib/datadog/core/configuration/base.rb'
   ignore 'lib/datadog/core/configuration/components.rb'
   ignore 'lib/datadog/core/configuration/dependency_resolver.rb'

lib/datadog/core/configuration/agent_settings_resolver.rb

@@ -19,17 +19,17 @@ module Configuration
       # Whenever there is a conflict (different configurations are provided in different orders), it MUST warn the users
       # about it and pick a value based on the following priority: code > environment variable > defaults.
       class AgentSettingsResolver
-        AgentSettings = Struct.new(
-          :adapter,
-          :ssl,
-          :hostname,
-          :port,
-          :uds_path,
-          :timeout_seconds,
-          keyword_init: true
-        ) do
-          def initialize(*)
-            super
+        # Immutable container for the resulting settings
+        class AgentSettings
+          attr_reader :adapter, :ssl, :hostname, :port, :uds_path, :timeout_seconds
+
+          def initialize(adapter: nil, ssl: nil, hostname: nil, port: nil, uds_path: nil, timeout_seconds: nil)
+            @adapter = adapter
+            @ssl = ssl
+            @hostname = hostname
+            @port = port
+            @uds_path = uds_path
+            @timeout_seconds = timeout_seconds
             freeze
           end
         end

sig/datadog/core/configuration/agent_settings_resolver.rbs

@@ -2,9 +2,8 @@ module Datadog
   module Core
     module Configuration
       class AgentSettingsResolver
-        class AgentSettings < ::Struct[untyped]
+        class AgentSettings
           def initialize: (adapter: untyped, ssl: untyped, hostname: untyped, port: untyped, uds_path: untyped, timeout_seconds: untyped) -> void
-          def merge: (**::Hash[untyped, untyped] member_values) -> AgentSettingsResolver
 
           attr_reader adapter: untyped
           attr_reader ssl: untyped
@@ -14,6 +13,17 @@ module Datadog
           attr_reader timeout_seconds: untyped
         end
 
+        @settings: untyped
+        @logger: untyped
+        @configured_hostname: untyped
+        @configured_port: untyped
+        @configured_ssl: untyped
+        @configured_timeout_seconds: untyped
+        @configured_uds_path: untyped
+        @uds_fallback: untyped
+        @mixed_http_and_uds: untyped
+        @parsed_url: untyped
+
         def self.call: (untyped settings, ?logger: untyped) -> untyped
 
         private
@@ -38,41 +48,49 @@ module Datadog
 
         def configured_uds_path: () -> untyped
 
-        def try_parsing_as_integer: (value: untyped, friendly_name: untyped) -> untyped
+        def parsed_url_ssl?: () -> (nil | untyped)
 
-        def try_parsing_as_boolean: (value: untyped, friendly_name: untyped) -> untyped
+        def try_parsing_as_integer: (value: untyped, friendly_name: untyped) -> untyped
 
-        def ssl?: () -> bool
+        def ssl?: () -> (false | untyped)
 
         def hostname: () -> untyped
 
         def port: () -> untyped
 
-        def uds_path: () -> untyped
-
         def timeout_seconds: () -> untyped
 
-        def uds_fallback: () -> untyped
+        def parsed_url_uds_path: () -> (nil | untyped)
 
-        def should_use_uds_fallback?: () -> untyped
+        def uds_path: () -> (nil | untyped)
 
-        def should_use_uds?: () -> bool
+        def uds_fallback: () -> untyped
 
-        def can_use_uds?: () -> bool
+        def should_use_uds?: () -> untyped
 
-        def parsed_url: () -> untyped
+        def mixed_http_and_uds: () -> untyped
 
-        def parsed_url_ssl?: () -> untyped
+        def can_use_uds?: () -> untyped
 
-        def parsed_url_uds_path: () -> untyped
+        def parsed_url: () -> untyped
 
         def pick_from: (*untyped configurations_in_priority_order) -> untyped
 
         def warn_if_configuration_mismatch: (untyped detected_configurations_in_priority_order) -> (nil | untyped)
 
         def log_warning: (untyped message) -> (untyped | nil)
 
+        def http_scheme?: (untyped uri) -> untyped
+
+        def parsed_http_url: () -> (untyped | nil)
+
+        def unix_scheme?: (untyped uri) -> untyped
+
         class DetectedConfiguration
+          @friendly_name: untyped
+
+          @value: untyped
+
           attr_reader friendly_name: untyped
 
           attr_reader value: untyped

sig/datadog/core/configuration/ext.rbs

@@ -15,6 +15,7 @@ module Datadog
         end
 
         module Agent
+          ENV_DEFAULT_HOST: 'DD_AGENT_HOST'
           ENV_DEFAULT_PORT: 'DD_TRACE_AGENT_PORT'
           ENV_DEFAULT_URL: 'DD_TRACE_AGENT_URL'
           ENV_DEFAULT_TIMEOUT_SECONDS: 'DD_TRACE_AGENT_TIMEOUT_SECONDS'