replace cast string to union function in driver.cpp

[AEsir777]

	new	old
UNION(v1 UINT8, v2 INT8, v3 INT64, v4 STRING) x 130000	1641.177	2002.431
UNION(v1 UINT8, v2 INT8, v3 INT64, v4 STRING) x 200000	1975.493	2481.309

[codecov]

Codecov Report

Attention: 40 lines in your changes are missing coverage. Please review.

Comparison is base (fc71a74) 89.58% compared to head (dba1a3b) 89.71%.
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2227      +/-   ##
==========================================
+ Coverage   89.58%   89.71%   +0.13%     
==========================================
  Files        1006     1012       +6     
  Lines       36313    35912     -401     
==========================================
- Hits        32530    32220     -310     
+ Misses       3783     3692      -91     

Files	Coverage Δ
src/binder/bind/bind_copy.cpp	94.83% <100.00%> (ø)
src/binder/bind/bind_create_macro.cpp	100.00% <100.00%> (+10.00%)	⬆️
src/binder/bind/bind_ddl.cpp	98.48% <100.00%> (+1.03%)	⬆️
src/binder/bind/bind_file_scan.cpp	98.46% <100.00%> (+1.44%)	⬆️
src/binder/bind/bind_graph_pattern.cpp	96.19% <100.00%> (+1.47%)	⬆️
src/binder/bind/bind_reading_clause.cpp	95.61% <100.00%> (-0.04%)	⬇️
src/binder/bind/bind_updating_clause.cpp	95.48% <100.00%> (ø)
...inder/bind_expression/bind_property_expression.cpp	93.33% <100.00%> (ø)
src/binder/binder.cpp	97.70% <100.00%> (-0.04%)	⬇️
src/binder/expression_binder.cpp	97.50% <100.00%> (-0.07%)	⬇️
... and 63 more

... and 53 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.