fix: preserve JSONC comments between name/colon and value/comma (#24)

[todor-a]

Fixes #24.

---

Transparency note: This PR was prepared with AI assistance (Claude).

---

Problem

Formatting JSONC silently drops comments that sit on their own line in a slot with no AST node to attach to, while still reporting success:

• between a property name and its colon (after-key)
• between a value and its trailing comma (after-value)

Reproduction from the issue (after-key and after-value at object spot 0 disappear):

{
  "k0"
  // after-key
  :
  // before-value
  "v0"
  // after-value
  ,
}

Cause

jsonc-parser keys each comment group by both the previous-token-end and the next-token-start. The generator, however, only emitted comments as leading (at a node start) or same-line trailing. Own-line comments in the two slots above (where the neighbouring token — colon or comma — is not an AST node) matched no emission path and were lost.

Fix

Emit those own-line comments as statements:

• gen_object_prop — after the colon (covers after-key, keyed at the name end, and own-line before-value, keyed at the value start).
• gen_comma_separated_value — before the comma (covers after-value; applies to both objects and arrays since they share this code).

Same-line comments keep their existing handling, so no other cases change. Line comments already emit ExpectNewLine, so no extra newline is pushed.

Tests

Added tests/specs/comments/Comments_PreservedBetweenTokens.txt with the exact issue reproduction plus an array variant. All specs pass and remain idempotent under format_twice.

[dsherret]

Thanks!