Port instance-data and single-quote LML fixes

[HassanAkbar]

Ports 4 verified fixes into the LML parser:

• Repeated blocks — multiple collection/import/export blocks accumulate instead of keeping only the last
• Empty instance body — {} → [], not a phantom attribute
• Attribute value — now typed Lutaml::Lml::LiteralValue (fixes serialization crash + map-key data loss)
• Single-quoted strings — now parse, including view X { import '...' }

Map values now serialize for real

value first moved to Type::Value. That kept the map keys but broke serialization.

• to_json raised ArgumentError.
• to_yaml emitted a !ruby/object tag.
• Document.from_yaml then refused to load it. That's the CLI's yaml input path.

The cause is upstream. lutaml-model's key-value serializer tests attribute_type < Type::Value, strictly. Type::Value isn't a strict subclass of itself, so it fell through to the raw-object branch.

LiteralValue is that subclass. It overrides #value to see through the wrapper the serializer adds.

• Maps survive to_json and to_yaml.
• They reload through Document.from_yaml and Document.from_json.
• Scalars, lists and nil behave exactly as before.

Round-trip claim, corrected

The earlier "round-trips cleanly" line only held for LML text and in-memory access. Map-valued documents now round-trip through JSON and YAML too.

Two limits stay, both pre-existing and unchanged:

• Array-valued attributes still fail Document.from_yaml.
• Four known map bugs are untouched: CSV column mapping, adapter stringification, quoted map keys, hydrate. Measured identical before and after.

Full suite: 490 examples, 0 failures.

[Copilot]

Pull request overview

This PR ports multiple parser/data-processing fixes into lutaml-lml to improve LML instance-data correctness and round-trip serialization, including repeated block accumulation, correct empty-body handling, map-valued attribute preservation, and support for single-quoted strings.

Changes:

• Accumulate repeated collection/import/export blocks in instance data instead of overwriting prior blocks.
• Fix instance attribute typing/processing to preserve map keys and avoid serialization type errors (e.g., to_yaml).
• Extend the grammar to parse single-quoted strings (validated via require '...').

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
spec/lutaml/lml/parser_spec.rb	Updates expectations for multiple collection blocks; adds regression coverage for map-valued attributes and serialization.
spec/lutaml/lml/grammar_spec.rb	Adds a test ensuring single-quoted require statements parse correctly.
spec/lutaml/lml/data_processor_spec.rb	Adds regression tests for empty attribute bodies and repeated instance block accumulation.
spec/fixtures/mixed_lml/instances.lml	Extends fixture instance data with a second collection block.
lib/lutaml/lml/models/top_element_attribute.rb	Retypes TopElementAttribute#value to a value wrapper to preserve map keys and avoid type issues.
lib/lutaml/lml/models/instance_collection.rb	Changes collections to a true collection attribute (array) to support repeated collection blocks.
lib/lutaml/lml/grammar/concerns/primitives.rb	Extends quoted_string to accept both double- and single-quoted strings.
lib/lutaml/lml/data_processor/instance_processing.rb	Refactors instance block processing to append/accumulate results across repeated blocks.
lib/lutaml/lml/data_processor/attribute_processing.rb	Ensures empty attribute arrays return [] (avoids phantom/incorrect structures).

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