fix: role detection; feat: set inside transactions

[levkk]

The role detection was pretty bad, it was causing an infinite loop on role change and DoSing itself. Now, we're using atomics on load balancer targets, so we don't need to reload the config when role changes.

For SET, we now handle it inside transactions and run it on the client's behalf. This makes it work when cross_shard_disabled = true. Additionally, all SET commands executed inside a transaction are rewritten to use SET LOCAL instead to avoid leaking client state between servers.

[codecov]

Codecov Report

❌ Patch coverage is 90.18868% with 52 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/frontend/client/test/mod.rs	0.00%	22 Missing ⚠️
pgdog/src/frontend/router/parser/query/set.rs	78.78%	7 Missing ⚠️
pgdog/src/backend/pool/shard/mod.rs	77.27%	5 Missing ⚠️
pgdog/src/backend/pool/connection/binding.rs	73.33%	4 Missing ⚠️
pgdog/src/backend/pool/lb/mod.rs	94.44%	4 Missing ⚠️
pgdog-config/src/core.rs	82.35%	3 Missing ⚠️
pgdog/src/frontend/client/query_engine/query.rs	62.50%	3 Missing ⚠️
pgdog/src/frontend/router/parser/query/test.rs	87.50%	2 Missing ⚠️
pgdog/src/backend/pool/shard/monitor.rs	66.66%	1 Missing ⚠️
pgdog/src/frontend/client/query_engine/set.rs	85.71%	1 Missing ⚠️

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[blacksmith-sh]

Found 1 test failure on Blacksmith runners:

Failure

Test	View Logs
crud_spec/CRUD and Join for Customer and Order does full CRUD and join	View Logs