Adapt to changes in the ADB ATO data source

[khaeru]

Closes #18.

In addition to the case mentioned in the issue description:

• "-", meaning presumably "no data".

…I also discovered:

• "41 226.2" —using a space as a thousands separator. The files as of 2023-04-17 contained only "," as a thousands separator.
• "10860 .6" —space before a decimal separator.
• "long ton" —apparently a unit descriptor copied into a data cell; sheet TAS-FRA-027 at Economy Code=MMR, TIME_PERIOD=2022. Note that this unit does not match the units annotation for the overall sheet.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.57%. Comparing base (d52312e) to head (1765e43). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #20 +/- ## ========================================== - Coverage 93.58% 93.57% -0.01% ========================================== Files 32 32 Lines 1184 1183 -1 ========================================== - Hits 1108 1107 -1 Misses 76 76 ``` | [Files with missing lines](https://app.codecov.io/gh/transport-data/tools/pull/20?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=transport-data) | Coverage Δ | | |---|---|---| | [transport\_data/adb/\_\_init\_\_.py](https://app.codecov.io/gh/transport-data/tools/pull/20?src=pr&el=tree&filepath=transport_data%2Fadb%2F__init__.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=transport-data#diff-dHJhbnNwb3J0X2RhdGEvYWRiL19faW5pdF9fLnB5) | `94.54% <100.00%> (+0.05%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/transport-data/tools/pull/20/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=transport-data)