Using sharesOf when getting vault shares on steth

[codecov[bot]]

Codecov Report

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

Project coverage is 82.05%. Comparing base (ae99a41) to head (bf714c5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1581 +/- ## ========================================== + Coverage 82.00% 82.05% +0.04% ========================================== Files 98 98 Lines 7236 7239 +3 ========================================== + Hits 5934 5940 +6 + Misses 1302 1299 -3 ``` | [Flag](https://app.codecov.io/gh/delvtech/agent0/pull/1581/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=delvtech) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/delvtech/agent0/pull/1581/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=delvtech) | `82.05% <100.00%> (+0.04%)` | :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=delvtech#carryforward-flags-in-the-pull-request-comment) to find out more.

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