fix: preserve matrix object identity

[luisleo526]

Summary

• give generic, bool, and numeric Pine matrices shared backing identity so ordinary assignment aliases the same matrix object
• retain an explicit detached copy() operation and preserve null/valid-empty behavior
• integrate matrix mutation checkpoints with historical rollback without weakening Release assertions

Root cause

The runtime wrappers owned matrix state by value. C++ assignment therefore detached the destination even though Pine matrix IDs are reference objects. That value behavior could be hidden by codegen-side UDT copies, typed method dispatch, and checkpoint restoration, so it was validated as independent factor D in the full A/B/C/D matrix.

Scope boundary

This PR changes only matrix object identity and its focused tests. It does not add direct-array UDT field support and does not modify strategy sources, TradingView tapes, settings, graders, or tier data. None of the seven changed paths has a Git LFS attribute.

Validation

• clean Release build: passed
• full CTest: 117/117 passed
• focused matrix identity target: passed
• exhaustive cross-repository N=4 gate: 16/16 cells, 80/80 probe executions, adjudicator GO
• git diff --check: clean

Companion milestones are merged: codegen #100 and exhaustive harness #119. The engine base already contains snapshot bridge #128 and Release assertion #129.

[Copilot]

Pull request overview

This PR updates Pine matrix wrappers to preserve PineScript-style matrix object identity (reference IDs) across ordinary C++ copies/assignments, while keeping copy() as the explicit detach operation. It also aligns snapshot/restore and Series tests with the new aliasing semantics.

Changes:

• Rework PineMatrix, PineGenericMatrix<T>, and PineGenericMatrix<bool> to share backing storage via std::shared_ptr, so copy/assignment aliases the same matrix ID.
• Update snapshot/restore to retain and mutate the original identity in-place (so existing aliases observe rollbacks), with explicit invalid-snapshot errors.
• Add/adjust focused tests covering identity, moves, snapshot behavior, and Series aliasing expectations.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_matrix_snapshot_compat.cpp	Updates snapshot compatibility assertions to reflect aliasing-on-assignment semantics.
tests/test_matrix_identity.cpp	New targeted test binary validating aliasing, detach via copy(), move semantics, and snapshot identity behavior.
tests/test_generic_matrix_series.cpp	Updates Series test to assert that history slots preserve matrix ID aliasing rather than value-detaching.
tests/CMakeLists.txt	Registers the new test_matrix_identity executable in the test suite.
src/matrix.cpp	Implements storage-backed identity, updated snapshot/restore, and routes operations through storage accessors.
include/pineforge/matrix.hpp	Switches PineMatrix to shared storage, defines identity-preserving move semantics, and snapshot identity retention.
include/pineforge/generic_matrix.hpp	Applies the same shared-identity model to generic and bool matrices, including snapshot identity retention and restore behavior.

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