sqldb+invoices: fix incorrectly stored invoice expiries when using native SQL

[bhandras]

Previously, when using the native schema, invoice expiries were incorrectly stored as 64-bit values (expiry in nanoseconds instead of seconds), causing overflow issues. Since we cannot determine the original values, we will set the expiries for existing invoices to 1 hour with this migration.

Based on https://github.com/lightningnetwork/lnd/pull/8854 only the last 5 commits are part of this PR.