Fix SQLite B-tree iterator

[davispuh]

Without this rows are being missed. This fixes #1.
Written by Claude but I tested that it now indeed works for me.

Bug Found: Missing Right-Most Pointer in Interior B-Tree Pages

The bug is in #iterateBTree. SQLite's B-tree interior pages (types 2 and 5) store N child pointers inside cells, plus one extra "right-most pointer" in the page header at offset +8. The current code iterates all cells but never follows this right-most pointer, so the entire rightmost subtree is silently skipped — causing rows to be missed for any table whose B-tree has interior pages.

Why this happens

SQLite interior B-tree pages have this structure:

Header (12 bytes for interior pages):
  +0  page type (1 byte)
  +1  first freeblock offset (2 bytes)
  +3  cell count (2 bytes)
  +5  cell content area offset (2 bytes)
  +7  fragmented free bytes (1 byte)
  +8  ► RIGHT-MOST POINTER (4 bytes)  ← was never read
  +12 cell pointer array starts here

Each cell in an interior page holds a left child pointer + a key. The right-most child (which contains all rows with keys greater than the last cell's key) is only stored in the header, not in any cell. For a table with N interior-page children, the loop visits N-1 of them and silently drops the last one — which can represent a large fraction of the rows.

[Copilot]

Pull request overview

This PR fixes SQLite B-tree traversal in SQLiteDatabase.#iterateBTree so that interior B-tree pages (types 2 and 5) also follow the page-header “right-most pointer”, preventing the rightmost subtree (and its rows) from being skipped.

Changes:

• After iterating all interior-page cells, additionally recurse into the interior page’s right-most child pointer at header offset +8.
• Ensures full table/index scans don’t miss rows that live in the rightmost branch of interior nodes.

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