fix: memory: fix Bytes move assignment ownership transfer

[xylaaaaa]

Purpose

Linked issue: close #xxx

Fix the move assignment of Bytes to avoid the ~Bytes() + memcpy pattern that can cause double-free/UB. The new implementation explicitly releases current memory, takes ownership from other, and then nulls out the source.

Tests

Not run.

API and Format

No API/storage/protocol changes (internal implementation only).

Documentation

No.

[Copilot]

Pull request overview

This PR fixes the move-assignment implementation of paimon::Bytes to avoid a destructor + memcpy pattern that could lead to double-free or undefined behavior and instead performs an explicit, safe ownership transfer.

Changes:

• Replace Bytes::operator=(Bytes&&) implementation from this->~Bytes(); memcpy; placement-new to explicit release of current buffer via pool_->Free followed by field-wise move of pool_, data_, and size_.
• Clear the moved-from Bytes object by nulling pool_ and data_ and zeroing size_ to make its destructor a no-op and avoid double-free.

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