refactor(source): remove Source trait

[neverchanje]

What's changed and what's your intention?

PLEASE DO NOT LEAVE THIS EMPTY !!!

We formerly defined a Source trait to generalize the construction of stream readers. However, table source and connector source are essentially different. The stream readers should be directly constructed via concrete type rather than using a trait.

After this refactoring, we can remove some prior efforts that tried to adapt the different constructions to the unified interface:

• TableV2ReaderContext
• ConnectorReaderContext
• SourceReaderContext

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Merging #2192 (3307ec4) into main (f684430) will increase coverage by 0.04%.
The diff coverage is 20.83%.

@@            Coverage Diff             @@
##             main    #2192      +/-   ##
==========================================
+ Coverage   70.89%   70.93%   +0.04%     
==========================================
  Files         650      650              
  Lines       82477    82555      +78     
==========================================
+ Hits        58470    58561      +91     
+ Misses      24007    23994      -13     

Flag	Coverage Δ
rust	70.93% <20.83%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/meta/src/cluster/mod.rs	59.39% <ø> (ø)
src/source/src/connector_source.rs	0.00% <0.00%> (ø)
src/source/src/lib.rs	87.50% <ø> (+24.53%)	⬆️
src/stream/src/executor_v2/source.rs	73.65% <0.00%> (+0.62%)	⬆️
src/source/src/manager.rs	45.74% <50.00%> (ø)
src/batch/src/executor2/delete.rs	79.50% <100.00%> (+0.47%)	⬆️
src/batch/src/executor2/insert.rs	80.82% <100.00%> (ø)
src/source/src/table_v2.rs	96.03% <100.00%> (+1.59%)	⬆️
src/connector/src/filesystem/file_common.rs	80.44% <0.00%> (-0.45%)	⬇️
.../src/executor/managed_state/aggregation/extreme.rs	90.02% <0.00%> (-0.27%)	⬇️
... and 6 more

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[tabVersion]

LGTM