rewrite: default inode-locking to no

rewrite: default inode-locking to no

Inode locking serializes FIDEDUPERANGE on the same inode by taking
per-inode mutexes for every ref of the dst/src extents before planning.
Measured behaviour shows this lowers overall dedupe throughput and
worsens IO efficiency: the task queue fills with work deferred while
waiting for an inode, so worker threads stall waiting for queue space,
and the added lock contention triggers more planner restarts, each of
which re-reads blocks.

Default the [rewrite] inode-locking option to no.  The feature is
retained for operators who want to reduce bees' external impact on
heavily accessed large files, where serializing dedupe per inode lowers
bees' competition with other readers and writers of the same file.

Only the authoritative default in bees-config-v2.cc changes; the C++
member initializer in bees.h is deliberately not kept in sync with
config defaults and the loader always overwrites it.

Assisted-by: Claude-Code:claude-opus-4-8