Fix matching of decoded span ids from profiles

Pprof decodes numeric labels as signed 64-bit values BUT as a slight
cheat both the profiler and the backend interpret them as unsigned
64-bit values so we can represent the full 64-bit values used for span
ids in traces.

But we were not accounting for this in our tests, so the decoded pprofs
we use for testing were not matching the expected values.

I've tweaked the pprof test reading code to account for this.

spec/datadog/profiling/spec_helper.rb

@@ -53,10 +53,8 @@ def samples_from_pprof(pprof_data)
         sample.location_id.map { |location_id| decode_frame_from_pprof(decoded_profile, location_id) },
         pretty_sample_types.zip(sample.value).to_h,
         sample.label.map do |it|
-          [
-            string_table[it.key].to_sym,
-            it.num == 0 ? string_table[it.str] : it.num,
-          ]
+          key = string_table[it.key].to_sym
+          [key, (it.num == 0 ? string_table[it.str] : ProfileHelpers.maybe_fix_label_range(key, it.num))]
         end.to_h,
       ).freeze
     end
@@ -103,6 +101,16 @@ def build_stack_recorder(
       timeline_enabled: timeline_enabled,
     )
   end
+
+  def self.maybe_fix_label_range(key, value)
+    if [:'local root span id', :'span id'].include?(key) && value < 0
+      # pprof labels are defined to be decoded as signed values BUT the backend explicitly interprets these as unsigned
+      # 64-bit numbers so we can still use them for these ids without having to fall back to strings
+      value + 2**64
+    else
+      value
+    end
+  end
 end
 
 RSpec.configure do |config|