Preserve comments through ConvertFrom-Yaml/ConvertTo-Yaml round-trip

[MariusStorhaug]

Why

ConvertFrom-Yaml discards all comments during parsing, and ConvertTo-Yaml has no concept of comments to emit, so a round-trip ConvertFrom-Yaml | ConvertTo-Yaml loses every # comment even though the YAML 1.2.2 spec treats comments as a valid presentation detail. A user editing a config file through this module should not have inline documentation silently deleted.

What

Preserve comments across a full round-trip:

$yaml | ConvertFrom-Yaml | ConvertTo-Yaml  # comments survive

This covers leading comments above a node, trailing comments on the same line as a key/value, and standalone comments between unrelated nodes.

Acceptance criteria

• A YAML file with a representative mix of comment kinds round-trips through ConvertFrom-Yaml | ConvertTo-Yaml byte-equivalent (or content-equivalent ignoring whitespace normalisation)
• Default behavior unchanged when comment preservation is not requested
• Spec test 2.9 (Single Document with Two Comments) passes a round-trip assertion

Related

• Add YAML 1.2.2 Chapter 2 spec-compliance test harness #20 (spec test harness) — once this lands, add a round-trip assertion to the relevant spec examples
• Support multi-document YAML streams #21 (multi-document streams) — comment preservation between documents depends on multi-doc support

[MariusStorhaug]

What changed: Reformatted the issue body to the MSXOrg Issue Format — a local Why plus an outcome-level What/acceptance criteria. Removed the Technical Decisions and Implementation Plan sections (and other implementation-tradeoff notes).
Why: Issue bodies should state local purpose and observable outcome without leaking implementation detail into the outcome-level description; durable technical decisions belong in the PR/design, not the tracking issue.
Follow-up: None.