perf: use shallow dup instead of deep_dup for Scope and BreadcrumbBuffer

⚠️ Needs closer review — changes copy semantics for scope containers.

Replace deep_dup with dup for Scope's contexts, extra, tags, user, and
fingerprint hashes, and for BreadcrumbBuffer's buffer array.

Rationale: These containers are not mutated in-place after duplication.
Scope methods like set_tags, set_extras, set_user all use assignment
(replacing the entire hash) or merge! on the copy's own hash. The inner
values (strings, numbers, symbols) are immutable or treated as such.

BreadcrumbBuffer: Individual Breadcrumb objects in the buffer are not
mutated after being recorded — they are only read during serialization.
A shallow dup of the buffer array is sufficient to prevent the copy
from seeing new breadcrumbs added to the original.

span, session, and propagation_context still use deep_dup as they
contain mutable nested state that may be modified in-place.

Author: HazAT

sentry-ruby/lib/sentry/breadcrumb_buffer.rb

@@ -57,7 +57,7 @@ def to_h
     # @return [BreadcrumbBuffer]
     def dup
       copy = super
-      copy.buffer = buffer.deep_dup
+      copy.buffer = buffer.dup
       copy
     end
   end

sentry-ruby/lib/sentry/scope.rb

@@ -124,13 +124,15 @@ def clear_breadcrumbs
     def dup
       copy = super
       copy.breadcrumbs = breadcrumbs.dup
-      copy.contexts = contexts.deep_dup
-      copy.extra = extra.deep_dup
-      copy.tags = tags.deep_dup
-      copy.user = user.deep_dup
+      # Shallow dup is sufficient for these containers — inner values are not
+      # mutated after scope duplication, only replaced via merge! or assignment
+      copy.contexts = contexts.dup
+      copy.extra = extra.dup
+      copy.tags = tags.dup
+      copy.user = user.dup
       copy.transaction_name = transaction_name.dup
       copy.transaction_source = transaction_source.dup
-      copy.fingerprint = fingerprint.deep_dup
+      copy.fingerprint = fingerprint.dup
       copy.span = span.deep_dup
       copy.session = session.deep_dup
       copy.propagation_context = propagation_context.deep_dup