Bucket query asserts and perf fix

[SirTyson]

Description

The first commit resolves #5067.

The 2nd commit addresses a perf issue we saw with the BucketList refactor. We build snapshot objects in parallel contents. Currently, the constructor gets a fresh set of metric references for each snapshot, acquiring a lock to do so. This changes it such that we use a single shared metrics object across all snapshots. Metrics are thread safe, so there should be no safety issue with this, and it makes the snapshot constructor much cheaper.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

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[Copilot]

Pull request overview

This PR improves BucketList snapshot safety and performance by (1) adding a test-build thread-ownership invariant to detect illegal cross-thread reuse of a single snapshot instance (per #5067), and (2) reducing snapshot/view construction overhead by sharing pre-resolved metric handles across views over the same immutable ledger state.

Changes:

• Add a threadInvariant() assertion path (BUILD_TESTS) to SearchableBucketListSnapshot query entry points to catch cross-thread snapshot reuse.
• Introduce BucketSnapshotMetrics and store shared metric references in ImmutableLedgerData so per-view snapshot construction avoids repeatedly taking the global metrics registry lock.
• Thread metrics registry through ImmutableLedgerData construction from LedgerManagerImpl.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/ledger/LedgerManagerImpl.cpp	Passes MetricsRegistry into ImmutableLedgerData construction sites.
src/ledger/ImmutableLedgerView.h	Extends ImmutableLedgerData to hold shared BucketSnapshotMetrics and updates ctor signature.
src/ledger/ImmutableLedgerView.cpp	Constructs shared snapshot metrics once per immutable state and wires them into ImmutableLedgerView snapshots.
src/bucket/BucketListSnapshot.h	Adds thread-invariant state (test builds) and introduces BucketSnapshotMetrics shared across snapshots.
src/bucket/BucketListSnapshot.cpp	Implements BucketSnapshotMetrics, shares metrics in snapshot ctor, and adds thread-invariant checks on query paths.