fix(query): avoid eager UID materialization on posting reads

[gooohgb]

Description

Related @matthewmcneely : #9807

This PR avoids eagerly materializing the full UID slice for posting lists on read paths where that work is not useful or actively bypasses existing optimizations.

Changes:

• Gate calculateUids() behind the posting-list cache being enabled, so --cache percentage=0,... does not build and immediately discard a full []uint64.
• Avoid using calculatedUids for bounded Uids() reads with First or Intersect, preserving early-stop and compressed-intersection paths.
• Reduce Uids() allocation size for bounded and small-intersect reads.
• Avoid GetUids() in worker paths that do not consume a full UID list, including count, scalar comparison, has, uid_in, facets, pagination, and intersect paths.

Checklist

• The PR title follows the
  Conventional Commits syntax, leading
  with fix:, feat:, chore:, ci:, etc.
• Code compiles correctly and linting (via trunk) passes locally
• Tests added for new functionality, or regression tests for bug fixes added as applicable

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}