feat: add process name to 2pc transaction ID + cleanup abandoned

[levkk]

Globally unique transaction ID

Without hopefully going over the 200 bytes limit.

Example:

__pgdog_2pc_pgdog-node-1_1231424234

The last part (the number) can be up to 20 chars long (usize::MAX), so I'm optimistic people don't name their nodes something 150 characters long, but I may be proven wrong.

Cleanup abandoned

Without durability, 2pc transactions can be left unfinished on PgDog crash/dirty shutdown. Leaving those around is bad: they can block vacuum.

TODO: need to add tests.

[codecov]

Codecov Report

❌ Patch coverage is 58.82353% with 70 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...src/frontend/client/query_engine/two_pc/manager.rs	18.60%	35 Missing ⚠️
.../client/query_engine/two_pc/server_transactions.rs	15.78%	16 Missing ⚠️
pgdog/src/main.rs	0.00%	7 Missing ⚠️
...src/backend/replication/logical/subscriber/copy.rs	0.00%	6 Missing ⚠️
...rc/frontend/client/query_engine/end_transaction.rs	0.00%	3 Missing ⚠️
...frontend/client/query_engine/two_pc/transaction.rs	88.88%	3 Missing ⚠️

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