Add two new configuration options for periodic retained WAL size check in scaled down mode

[alco]

This PR introduces periodic monitoring of retained WAL size when Electric has scaled down its database connections due to inactivity. If during one of these periodic checks the retained WAL is detected to have grown beyond the configured threshold, Electric wakes up the connection subsystem to resume replication stream processing.

Core changes

Connection.Restarter

• When connections scale down, starts a periodic timer to check retained WAL size
• Queries Postgres for the retained WAL size using pg_wal_lsn_diff(pg_current_wal_lsn(), restart_lsn)
• If size exceeds threshold, restarts the connection subsystem
• Logs checks with human-readable sizes and intervals

Connection.Manager
When it validates connection options, it stores the validated ones in StackConfig. This can then be used by Connection.Restarter for one-off DB queries to check the retained WAL size. When Connection.Manager restarts (after an error or when the connection subsystem is woken up), it erases these options from StackConfig and repeats the validation process as before. This is to prevent the system from ending up in an invalid state by ensuring that at Connection.Manager startup it will always get the same starting connection options to work with.

Added two new configuration options:

• ELECTRIC_REPLICATION_IDLE_WAL_SIZE_CHECK_PERIOD: How often to check retained WAL size when scaled down (default: 1 hour)
• ELECTRIC_REPLICATION_IDLE_WAL_SIZE_THRESHOLD: WAL size threshold that triggers reconnection (default: 100 MB)

Both options support human-readable time/size formats.

Refactoring

Introduced a new module name OneOffConnection that wrap Postgrex.SimpleConnection and provides a simple API for opening a one-off DB connection, running a query (using the simple protocol) and getting the result back, all synchronously.

Reimplemented the lock breaking logic using OneOffConnection and removed LockBreakerConnection since it was no longer necessary to have as a separate module.

Refactored ConnectionResolver, replacing its ad-hoc wrapping of Postgrex.SimpleConnection with OneOffConnection.

Testing

Added a new integration test (integration-tests/tests/wal-size-check-while-scaled-down.lux) that verifies Electric's handling of two cases during its periodic WAL size check: 1) WAL size under the threshold; 2) WAL size has exceeded the threshold.

---

Closes #3260.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.76%. Comparing base (de615ef) to head (9d32a33).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3274      +/-   ##
==========================================
- Coverage   87.79%   87.76%   -0.03%     
==========================================
  Files          18       18              
  Lines        1663     1676      +13     
  Branches      420      425       +5     
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+ Hits         1460     1471      +11     
- Misses        201      203       +2     
  Partials        2        2              

Flag	Coverage Δ
packages/experimental	87.73% <ø> (ø)
packages/react-hooks	86.48% <ø> (ø)
packages/typescript-client	93.66% <ø> (-0.10%)	⬇️
packages/y-electric	56.05% <ø> (ø)
typescript	87.76% <ø> (-0.03%)	⬇️
unit-tests	87.76% <ø> (-0.03%)	⬇️

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[msfstef]

Looks good but I assume this does not work since there's no querying of the wal size (and no tests which I assume is for the above reason?)