walletFactory heap is still growing after u18

[mhofman]

Describe the bug

Investigating the wallet factory leak in u17 and before (#10706), we identified an issue (#10757) and implemented a workaround for it (#10756), however from preliminary observations of the wallet factory heap in u18 on devnet, there is still a remaining leak.

To Reproduce

Observe the uncompressedSize of heap-snapshot-save slog entries for the walletFactory vat.

Expected behavior

Heap size flat over time

[aj-agoric]

Added this to U19 for nearterm tracking. Its a P2 already, so we can easily prioritize this out if needed.