[improve][ml] Open ledgers through the BookKeeper builder API - #26598

Every ledger open in managed-ledger still went through the legacy
BookKeeper.asyncOpenLedger / asyncOpenLedgerNoRecovery overloads, while
ledger creation already uses newCreateLedgerOp(). The builder API is
where BookKeeper adds per-ledger options (4.18.1 ships
OpenBuilder.withKeepUpdateMetadata and withOrderingKey), so this moves
the remaining opens to newOpenLedgerOp() without changing behavior.

The three opens that passed keepUpdateMetadata=true (ManagedLedgerImpl
init-time open and concurrent-modification recheck, ManagedCursorImpl
cursor-ledger recovery) use withRecovery(true).withKeepUpdateMetadata(true),
which maps onto the same LedgerOpenOp.initiateWithKeepUpdateMetadata()
path. The no-recovery opens in ShadowManagedLedgerImpl and the
offline-stats cursor read in ManagedLedgerFactoryImpl use
withRecovery(false). The existing OpenCallback bodies are kept and fed
from the returned future, casting the handle to LedgerHandle as the real
client returns a ReadOnlyLedgerHandle.

PulsarMockBookKeeper's open builder returned a plain ReadHandle, which
cannot be cast to the LedgerHandle the managed ledger and cursor keep.
PulsarMockReadHandle is now a read-only LedgerHandle sharing the
writer's entries, like ReadOnlyLedgerHandle: close is a no-op, reads
still go through the read interceptor, it honors the mock's empty-ledger
countdown, and the legacy asyncReadEntries is shared with the write
handle. The mock's open builder completes on the mock executor, as the
legacy mock path and the real client do. ManagedCursorTest and
ManagedLedgerFactoryShutdownTest intercept newOpenLedgerOp() instead of
the legacy overloads.

The managed ledger now opens its last ledger and the cursor ledgers
through newOpenLedgerOp() when a topic is reloaded, so the open-builder
stub in this test also records those opens. Clear the recorded set right
before compacting, and expect the penultimate ledger to have been opened
for its stats after the reload, as the comment already said.

… writes on the mock read view

Review follow-ups:

- The builder-based opens bridge their future to the legacy OpenCallback
  with whenComplete and dropped the returned stage, so anything the
  callback threw (for example a RejectedExecutionException when the
  managed ledger executor is already shut down) was swallowed instead of
  being logged the way BookKeeper's executor did. All six sites now go
  through ManagedLedgerImpl.completeOpenCallback, which logs it.
- PulsarMockBookKeeper.newOpenLedgerOp() used thenComposeAsync, which
  short-circuits on an already failed programmed-failure future and
  completed the open inline on the caller's thread. It now always
  completes on the mock executor, as the legacy mock open path did.
- PulsarMockReadHandle rejects writes with IllegalOpException, like
  ReadOnlyLedgerHandle, instead of falling through to LedgerHandle's
  write path and the mock's null client internals.