(feat): Header Gradient added.

[Swado]

Fixes #72

• Added new field: Introduced a new field named headingRowDecoration in async_paginated_data_table_2, data_table_2, and paginated_data_table_2.
• Field Type: This new field is of type BoxDecoration.
• Overrides: It serves as an override for both headingRowColor and fixedCornerColor.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.05% :tada:

Comparison is base (baf9357) 95.66% compared to head (2ed28a4) 95.71%. Report is 2 commits behind head on main.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #220 +/- ## ========================================== + Coverage 95.66% 95.71% +0.05% ========================================== Files 3 3 Lines 1107 1121 +14 ========================================== + Hits 1059 1073 +14 Misses 48 48 ``` | [Files Changed](https://app.codecov.io/gh/maxim-saplin/data_table_2/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Maxim+Saplin) | Coverage Δ | | |---|---|---| | [lib/src/async\_paginated\_data\_table\_2.dart](https://app.codecov.io/gh/maxim-saplin/data_table_2/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Maxim+Saplin#diff-bGliL3NyYy9hc3luY19wYWdpbmF0ZWRfZGF0YV90YWJsZV8yLmRhcnQ=) | `85.11% <ø> (ø)` | | | [lib/src/data\_table\_2.dart](https://app.codecov.io/gh/maxim-saplin/data_table_2/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Maxim+Saplin#diff-bGliL3NyYy9kYXRhX3RhYmxlXzIuZGFydA==) | `98.37% <100.00%> (+0.02%)` | :arrow_up: | | [lib/src/paginated\_data\_table\_2.dart](https://app.codecov.io/gh/maxim-saplin/data_table_2/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Maxim+Saplin#diff-bGliL3NyYy9wYWdpbmF0ZWRfZGF0YV90YWJsZV8yLmRhcnQ=) | `97.94% <100.00%> (+0.03%)` | :arrow_up: |

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[maxim-saplin]

Thanks! Will be checking tomorrow

[maxim-saplin]

Looks good, thank you for the contribution!