Add unordered hashtable projection mode

[MariusStorhaug]

Context

PowerShell users often want YAML mappings as unordered Hashtable values rather than ordered dictionaries or objects. This is a projection capability, not a YAML conformance requirement, but it affects how rich objects flow through the pipeline.

Official YAML 1.2.2 reference:

• Mapping model: https://yaml.org/spec/1.2.2/#3211-nodes
• Mapping key order as serialization detail: https://yaml.org/spec/1.2.2/#3221-mapping-key-order
• Normative module spec: spec/Hashtable-Projection.md

Current State

The module can project mappings as objects or insertion-ordered dictionaries. There is no dedicated unordered hashtable projection mode.

Objective

Add an idiomatic PowerShell projection option for unordered hashtables while preserving existing object and ordered-dictionary behavior.

PowerShell Design Considerations

• Parameter sets should make object, ordered dictionary, unordered hashtable, and future typed projection choices mutually clear.
• Hashtable projection should be useful in normal pipeline workflows and splatting scenarios.
• Complex or non-string YAML keys need explicit behavior because ordinary PowerShell hashtables can technically hold object keys but may surprise users.
• Do not use hashtable projection to bypass duplicate representation-key validation.

Tasks

• Add an explicit hashtable projection option.
• Define how nested mappings project under that option.
• Preserve existing default object projection and ordered dictionary projection.
• Define behavior for complex, null, empty, and case-colliding keys.
• Document pipeline and splatting examples.

Benefits

• Better matches common PowerShell authoring patterns.
• Makes projection choice explicit and discoverable.
• Avoids forcing users to convert ordered dictionaries manually.

Acceptance Criteria

• A mapping can be returned as a Hashtable when the caller requests it.
• Nested mappings follow the requested projection policy.
• Duplicate YAML representation keys still fail before hashtable projection.
• Existing default and ordered projection behavior remain unchanged.
• Parameter-set help makes projection modes clear.

Related

• Spec folder: spec/Hashtable-Projection.md