Write boolean stats for boolean columns (not i32 stats)

[alamb]

Which issue does this PR close?

Resolves #659

Rationale for this change

Bool columns were writing the wrong type of statistics

What changes are included in this PR?

Write boolean stats for boolean columns (not i32 stats)

Are there any user-facing changes?

Statistics for bool columns in parquet files are now boolean. I am not sure if this is visible to users though, as when I used parquet-tools to create a parquet file with a boolean column, the min/max statistics look correct to me (aka are boolean)

alamb@MacBook-Pro rust_parquet % parquet-tools dump -n  /tmp/test_bool.parquet 
parquet-tools dump -n  /tmp/test_bool.parquet 
row group 0 
------------------------------------------------------------------------------------------------------------------
bool_col:  BOOLEAN UNCOMPRESSED DO:0 FPO:4 SZ:40/40/1.00 VC:6 ENC:PLAIN,RLE ST:[min: false, max: true, num_nulls: 1]

    bool_col TV=6 RL=0 DL=1
    --------------------------------------------------------------------------------------------------------------
    page 0:  DLE:RLE RLE:RLE VLE:PLAIN ST:[min: false, max: true, num_nulls: 1] CRC:[none] SZ:7 VC:6

BOOLEAN bool_col 
------------------------------------------------------------------------------------------------------------------
*** row group 1 of 1, values 1 to 6 *** 
value 1: R:0 D:1 V:true
value 2: R:0 D:1 V:true
value 3: R:0 D:1 V:false
value 4: R:0 D:0 V:<null>
value 5: R:0 D:1 V:false
value 6: R:0 D:1 V:true
alamb@MacBook-Pro rust_parquet %