fixes

[hawjo01]

• Reduce the number of TextSpan elements in a Tooltip
• Rename heartRate to pulse

[github-actions]

LCOV of commit ecf9362 during Analyze and Test on Pull Request #39

Summary coverage rate:
  lines......: 54.5% (246 of 451 lines)
  functions..: no data found
  branches...: no data found

Files changed coverage rate:
                                          |Lines       |Functions  |Branches    
  Filename                                |Rate     Num|Rate    Num|Rate     Num
  ==============================================================================
  lib/db/record.dart                      | 0.0%     17|    -     0|    -      0
  lib/db/record_repository.dart           | 0.0%     33|    -     0|    -      0
  lib/record_input_screen.dart            |    -      0|    -     0|    -      0
  lib/widgets/records_line_chart.dart     | 0.0%     63|    -     0|    -      0
  lib/widgets/records_table.dart          | 0.0%     13|    -     0|    -      0