Minor fixes and improvements.

Changes

• Do not try to cleanup statements (#981)
  (by @fvannee in d2e710f for #981)

• Add Pool.is_closing() method (#973)
  (by @singingwolfboy in 9cb2c1c for #973)

• Fix test_tls_version for LibreSSL (#974)
  (by @CyberTailor in 7df9812 for #974)

• Handle environments without home dir (#1011)
  (by @LeonardBesson in 172b8f6 for #1011)

• fix: salt and iterations parsing for scram (#1026)
  (by @trigonometr in 7443a9e for #1026)

• Add support for target_session_attrs (#987)
  (by @JesseDeLoore in bf74e88 for #987)

• Add support for READ UNCOMMITTED (#1039)
  (by @benwah in 2f20bae for #1039)

• Update benchmarks, add psycopg3 (#1042)
  (by @elprans in 7d4fcf0 for #1042)