feat: log the execution plan in a more compact fashion

[westonpace]

Currently we log the debug representation of the plan (twice!) every time a plan is executed. This is way too much information (e.g. the object store's debug information is repeated many times). In one egregious case I was dealing with that had 8k fragments this was generating 35MB of log data!

This PR changes to an indented display representation of the plan.

[westonpace]

Example output:

[2024-09-18T13:41:35Z DEBUG lance_file::v2::writer] write_batch called with 80096 bytes of data
[2024-09-18T13:41:35Z DEBUG lance_datafusion::exec] Executing plan:
    ProjectionExec: expr=[x@0 as x]
      FilterExec: x@0 = 7
        LanceScan: uri=tmp/foo.lance/data, projection=[x], row_id=true, row_addr=false, ordered=true
    
[2024-09-18T13:41:35Z DEBUG lance::io::exec::scan] Given io_parallelism=8 and num_columns=1 we will read 16 fragments at once while scanning v2 dataset

One potential concern here is that we are generating more than one line of info. This is much more human readable but could potentially upset simple log parsers that assume each newline is a new line of log info.

However, I think more sophisticated log parsers will be able to detect the newline + timestamp pattern as the start of a line.

But I'd be open to changing it to one line if anyone felt strongly.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.96%. Comparing base (73599c5) to head (1ce57dc).

Files with missing lines	Patch %	Lines
rust/lance-datafusion/src/exec.rs	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2906      +/-   ##
==========================================
+ Coverage   77.93%   77.96%   +0.03%     
==========================================
  Files         231      231              
  Lines       70641    70643       +2     
  Branches    70641    70643       +2     
==========================================
+ Hits        55051    55074      +23     
+ Misses      12439    12437       -2     
+ Partials     3151     3132      -19     

Flag	Coverage Δ
unittests	77.96% <33.33%> (+0.03%)	⬆️

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