Fix pool topology error names

[Mirochill]

Summary

• add correctly spelled PoolTopologyError and PoolTopologyWarning names
• update connection pool code and tests to use the corrected names
• keep PoolTolopogyError and PoolTolopogyWarning as backward-compatible aliases

Fixes #332.

Validation

• git diff --check
• git diff --cached --check
• git diff --check HEAD~1..HEAD
• git show --check --stat HEAD
• Not run locally: project tests, lint, build, install, or Tarantool runtime