Clamp Forknote2 merge-mining depth during deserialize

[MoneroOcean]

Motivation

• Prevent untrusted tx_extra_merge_mining_tag.depth from causing unbounded std::vector allocation during Forknote2 parent-block deserialization, which can be triggered by daemon-controlled block templates and lead to OOM/abort.

Description

• Add a defensive check in src/cryptonote_basic/cryptonote_basic.h that returns false if mm_tag.depth exceeds MAX_MERGE_MINING_DEPTH (set to 128) before calling PREPARE_CUSTOM_VECTOR_SERIALIZATION(mm_tag.depth, ...), rejecting malformed inputs early.

Testing

• No automated build or unit test suite was run in this environment; the patch was applied and committed successfully (git commit completed).

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Codex Task