Add mapData extension to transform the StockResponse<T> into a StockResponse<E>

[codecov-commenter]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (637e672) compared to base (deb12dd). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #31 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 14 14 Lines 230 230 ========================================= Hits 230 230 ``` | [Impacted Files](https://codecov.io/gh/xmartlabs/stock/pull/31?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xmartlabs) | Coverage Δ | | |---|---|---| | [...extensions/stock\_response\_internal\_extensions.dart](https://codecov.io/gh/xmartlabs/stock/pull/31/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xmartlabs#diff-bGliL3NyYy9leHRlbnNpb25zL3N0b2NrX3Jlc3BvbnNlX2ludGVybmFsX2V4dGVuc2lvbnMuZGFydA==) | `100.00% <100.00%> (ø)` | | | [lib/src/stock\_response\_extensions.dart](https://codecov.io/gh/xmartlabs/stock/pull/31/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xmartlabs#diff-bGliL3NyYy9zdG9ja19yZXNwb25zZV9leHRlbnNpb25zLmRhcnQ=) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xmartlabs). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xmartlabs)

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