Preserve original collection fragments for callbacks

[OskarEichler]

Summary

Capture the collection before processing so setters/filters see neither the previous property nor the last hash item. Restore the parent hash fragment in ensure without a context copy per item. Addresses #231.

Reproduction

require 'representable/hash'
klass=Class.new(Representable::Decorator) do
  include Representable::Hash
  property :first
  collection :items, setter: ->(fragment:, represented:, **) { represented.items=fragment }
end
p klass.new(Struct.new(:first,:items).new).from_hash('first'=>'earlier','items'=>[1,2]).items
# 'earlier' before; [1,2] after

Verification

• Existing master suite on this isolated branch: 545 tests / 701 assertions, zero failures/errors, three existing skips on Ruby 3.2.11. Ruby 4.0.6 retains the same eight legacy inspection-format failures, zero errors and three skips. Existing tests/expectations are unchanged.
• 200 focused checks on Ruby 3.2.11/4.0.6 for this change. XML first-render uses a separate fresh-process check.
• Combined release-based verification with other focused fixes and attributed Use Setter in OverwriteOnNil if a :setter is defined #177/Hash value of null breaks parsing #264/Update MultiJSON usage to address deprecations #273 source backports: 544 tests / 700 assertions pass on Ruby 3.2.11, plus 4,410 focused checks and 36 boundary checks. Package retains 104 paths and unchanged compared metadata. All 36 runtime files compile on both Rubies; no newly introduced default Lint offenses.

The initial per-item dup prototype was rejected after it regressed hash rendering. The final restore-in-ensure approach preserves allocations for the 100-entry hash-collection workload (202,000 per 1,000 calls); combined-patch median time 0.021622→0.020985s. A separate hash-render workload is 0.010262→0.010458s with one extra options Hash per render from the separate caller-options fix. These are local YJIT measurements, not a production performance guarantee.

Breaking changes / limitations

Post-collection callbacks receive the original collection fragment. Item fragments still work; other existing shared hash callback state remains shared. Fragment restoration also occurs when an item raises.

No new/modified checked-in tests. Ruby 2.4–3.1, JRuby, Windows and Linux were not executed locally. Ruby >=2.4 and runtime dependency ranges remain unchanged. External test tooling supplies a legacy MiniTest alias and ruby-prof 1.7.x; no assertions were changed. No production verification is claimed.