Add lazy object key index

[iDavi]

Summary

• build normalized object-key entries lazily after repeated lookups on wide objects
• keep the direct sibling scan for the first lookup and small objects
• use late-bound Scripting.Dictionary so no project reference is required
• normalize escaped JSON member names while building the index

Why

Repeated reads from wide objects scanned all sibling tokens for every key lookup. The lazy index provides expected constant-time lookup after its one-time build.

Notes

This overlaps the escaped-member-name normalization in #7; merge/rebase #7 first if both drafts are accepted.

Validation

• reviewed index creation, duplicate-key first-match behavior, and document-reset lifecycle statically
• no VBA runtime or test suite is available in this environment

Closes #2