Fix repr on Base class

[sdhiscocks]

Add new argument for fillvalue and indent that cause error if missing in some cases

Primarily errors were with indent that was introduced in Python 3.12

[codecov[bot]]

Codecov Report

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

Project coverage is 94.09%. Comparing base (35ec8fd) to head (e3317f9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1049 +/- ## ======================================= Coverage 94.09% 94.09% ======================================= Files 204 204 Lines 13351 13353 +2 Branches 2731 2730 -1 ======================================= + Hits 12562 12565 +3 Misses 533 533 + Partials 256 255 -1 ``` | [Flag](https://app.codecov.io/gh/dstl/Stone-Soup/pull/1049/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | Coverage Δ | | |---|---|---| | [integration](https://app.codecov.io/gh/dstl/Stone-Soup/pull/1049/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | `67.36% <75.00%> (-0.06%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/dstl/Stone-Soup/pull/1049/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | `90.13% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl#carryforward-flags-in-the-pull-request-comment) to find out more.

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