Picks up the _txlock=immediate DSN fix from libfossil#33/#34 so concurrent writers serialize at BEGIN (where busy_timeout applies) instead of racing the SHARED→RESERVED upgrade.

Required upstream for sesh's --scope=project mode to remain safe after sesh drops its direct libfossil/db/driver/modernc require. Without this bump, EdgeSync's hub init() (added in v0.0.18) would register a pre-fix driver and consumers regress on contention.

Closes #167.

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