Polaris persistence concurrency issues

[snazy]

Describe the bug

As pointed out on the mailing list, the current persistence implementation in Polaris, even if run with the required isolation level, yields errors like ERROR: could not serialize access due to read/write dependencies among transactions. The underlying test case, which runs concurrent modifications to different Iceberg tables (non-conflicting changes) and did not "overload" Polaris, should really never yield such errors to users.

This issue could be a consequence of #775, assuming that the behavior of one persistence backend can be ported 1:1 to another one.

To Reproduce

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Actual Behavior

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Expected Behavior

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Additional context

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System information

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