Fix decimal repr in parquet schema printer

[sergiimk]

Which issue does this PR close?

Closes #713.

Rationale for this change

Formatting of DECIMAL in schemas where only ConvertedType is present and not LogicalType was broken.
This is the case for parquet files produced by Spark.

What changes are included in this PR?

I also had to update decimal_length_from_precision function as the math there seemed off.
When used as .with_length(decimal_length_from_precision(19)) it resulted in a panic:

Cannot represent FIXED_LEN_BYTE_ARRAY as DECIMAL with length 8 and precision 19. The max precision can only be 18

Are there any user-facing changes?

print_schema will no longer produce malformed results for decimals.

[codecov-commenter]

Codecov Report

Merging #721 (4ab1a14) into master (5a12d97) will increase coverage by 0.01%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #721      +/-   ##
==========================================
+ Coverage   82.50%   82.51%   +0.01%     
==========================================
  Files         168      168              
  Lines       47589    47597       +8     
==========================================
+ Hits        39261    39273      +12     
+ Misses       8328     8324       -4     

Impacted Files	Coverage Δ
parquet/src/schema/printer.rs	74.65% <83.33%> (+1.95%)	⬆️
parquet/src/encodings/encoding.rs	94.48% <0.00%> (-0.20%)	⬇️

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[houqp]

good catch, this is where named argument passing would be really helpful >_<

[alamb]

Thank you for the contribution @sergiimk ! I can't say I am an expert in this area of the parquet but the test looks good so given CI passes, looks good to me

@sunchao FYI

[alamb]

In case anyone is interested, I double checked that test fails without the code change in this PR (unsurprisingly):

---- schema::printer::tests::test_print_flba_logical_types stdout ----
thread 'schema::printer::tests::test_print_flba_logical_types' panicked at 'called `Result::unwrap()` on an `Err` value: General("Cannot represent FIXED_LEN_BYTE_ARRAY as DECIMAL with length 8 and precision 19. The max precision can only be 18")', parquet/src/schema/printer.rs:644:18