Added format conversion caching when Serializing/Deserializing

[HassanAkbar]

fixes #267

[Copilot]

Pull request overview

Adds an opt-in, store-backed caching layer for format conversions to reduce repeated serialization/deserialization work (fixes #267), with configuration, documentation, and test coverage.

Changes:

• Introduces cache_conversions + with_conversion_cache to cache from_* results (model instances) and to_* results (serialized strings).
• Adds Lutaml::Model::Config.conversion_cache with lazy auto-detection of a default in-memory Lutaml::Store::BasicStore when lutaml-store is loaded, plus global disable via false.
• Documents conversion caching behavior and adds comprehensive specs for cache key semantics, opt-in behavior, and backend quirks (e.g., CacheStore JSON round-tripping).

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
spec/lutaml/model/conversion_caching_spec.rb	New specs covering caching behavior, key separation, disablement, and backend error propagation.
README.adoc	Adds a feature bullet and a new “Conversion caching” section referencing the dedicated doc.
lib/lutaml/model/serialize/format_conversion.rb	Wraps from/to conversions with the caching layer.
lib/lutaml/model/serialize/conversion_caching.rb	New caching implementation (keying, payload digesting, store integration).
lib/lutaml/model/serialize.rb	Autoloads/includes the caching module into Serializable class methods.
lib/lutaml/model/configuration.rb	Adds conversion_cache config with lazy default store auto-detection.
lib/lutaml/model/config.rb	Exposes Config.conversion_cache getter/setter API.
Gemfile	Adds lutaml-store for development/test usage.
docs/conversion_caching.adoc	New detailed documentation for activation rules, semantics, and limitations.

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