refactor: Factor out logic for re-use by new streaming CSV source

[nameexhaustion]

Some prep work.

• Adds support parsing Time when using scan_csv - currently it only worked with read_csv
• Adds a POLARS_FORCE_NEW_STREAMING flag

[codecov]

Codecov Report

Attention: Patch coverage is 94.21965% with 10 lines in your changes missing coverage. Please review.

Project coverage is 79.91%. Comparing base (0f64785) to head (9711fbf).
Report is 42 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-io/src/csv/read/reader.rs	88.63%	5 Missing ⚠️
crates/polars-lazy/src/frame/mod.rs	66.66%	2 Missing ⚠️
...rates/polars-time/src/chunkedarray/string/infer.rs	81.81%	2 Missing ⚠️
crates/polars-io/src/csv/read/schema_inference.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19637      +/-   ##
==========================================
- Coverage   79.92%   79.91%   -0.02%     
==========================================
  Files        1536     1536              
  Lines      211686   211670      -16     
  Branches     2445     2445              
==========================================
- Hits       169192   169156      -36     
- Misses      41939    41959      +20     
  Partials      555      555              

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[ritchie46]

As a side effect this also adds support parsing Time when reading CSV.

How come?

No logical changes further? E.g. no perf changes.