fix(runtime): make AudioFrame copies own their sample data

[wangxiuwen]

What does this PR do?

Complete AudioFrame's copy ownership semantics:

• Deep-copy the owned sample buffer in the copy constructor.
• Copy global_start and global_end metadata.
• Add a deep-copy assignment operator with self-assignment and allocation-failure guards.

Why is this needed?

AudioFrame owns data and releases it in its destructor. The existing copy constructor copied only part of the metadata and silently dropped the sample buffer. The implicit copy-assignment operator was more dangerous: it shallow-copied the owned pointer, allowing two frames to free the same allocation.

Implementing both copy operations keeps the existing copyable API while giving each frame independent ownership of its samples.

Validation

• git diff --check
• Verified the copy constructor and assignment operator copy all frame fields.
• Verified self-assignment leaves the frame unchanged.
• Verified assignment allocates the replacement before releasing the destination buffer.
• Verified AudioFrame copy operations are not currently used by the in-tree runtime call sites, so this does not change hot-path behavior.

[gemini-code-assist]

Caution

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