Improve CodeLens tests

[st0012]

1. Fix CodeLens's listener test cleanup logic. It was incorrectly cleaning up Hover's listeners.
2. Improve empty responses' assertion logic.

[github-actions]

Benchmark results in seconds (slowest at top)

          textDocument/completion average: 0.261449 std_dev: 0.004934
          textDocument/diagnostic average: 0.038718 std_dev: 0.009243
      textDocument/selectionRange average: 0.003287 std_dev: 0.000434
   textDocument/documentHighlight average: 0.001677 std_dev: 0.000129
        textDocument/documentLink average: 0.001668 std_dev: 0.000107
            textDocument/codeLens average: 0.001667 std_dev: 0.000113
 textDocument/semanticTokens/full average: 0.001665 std_dev: 0.000283
      textDocument/documentSymbol average: 0.001661 std_dev: 6.8e-05
        textDocument/foldingRange average: 0.001456 std_dev: 9.2e-05
textDocument/semanticTokens/range average: 0.000852 std_dev: 4.3e-05
           textDocument/inlayHint average: 0.000599 std_dev: 3.7e-05
               codeAction/resolve average: 0.000566 std_dev: 6.3e-05
               textDocument/hover average: 0.000532 std_dev: 5.7e-05
    textDocument/onTypeFormatting average: 0.000103 std_dev: 5.2e-05
          textDocument/formatting average: 6.2e-05 std_dev: 0.00028
          textDocument/codeAction average: 3.5e-05 std_dev: 2.7e-05


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Comparison with main branch:

 textDocument/semanticTokens/full unchanged
textDocument/semanticTokens/range unchanged
      textDocument/documentSymbol unchanged
        textDocument/foldingRange unchanged
          textDocument/formatting unchanged
          textDocument/diagnostic unchanged
        textDocument/documentLink unchanged
           textDocument/inlayHint unchanged
      textDocument/selectionRange unchanged
   textDocument/documentHighlight unchanged
               textDocument/hover unchanged
          textDocument/codeAction unchanged
    textDocument/onTypeFormatting unchanged
               codeAction/resolve unchanged
          textDocument/completion unchanged
            textDocument/codeLens unchanged