fix: [branch-0.10][iceberg] Close reader instance in ReadConf

[andygrove]

Which issue does this PR close?

Backport #2510 to branch-0.10

Rationale for this change

What changes are included in this PR?

How are these changes tested?

[andygrove]

@hsiang-c fyi

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (branch-0.10@42f6774). Learn more about missing BASE report.

Additional details and impacted files

@@              Coverage Diff               @@
##             branch-0.10    #2535   +/-   ##
==============================================
  Coverage               ?   57.89%           
  Complexity             ?     1401           
==============================================
  Files                  ?      147           
  Lines                  ?    13501           
  Branches               ?     2378           
==============================================
  Hits                   ?     7816           
  Misses                 ?     4449           
  Partials               ?     1236           

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