misc: Add toString() to OutputBuffer stats (#11562) #15331

Job	Run time
Build	48m 47s
Build with Clang	0s
Spark Aggregate Fuzzer	15m 48s
Exchange Fuzzer	16m 14s
Presto Bias Fuzzer	0s
Biased Aggregation Fuzzer with Presto as source of truth	0s
Presto Fuzzer	30m 59s
Aggregation Fuzzer with Presto as source of truth	22m 36s
Join Fuzzer	17m 36s
Window Fuzzer with Presto as source of truth	18m 21s
Biased Expression Fuzzer with Only Added/Updated Functions and Presto as source of truth	0s
Writer Fuzzer with Presto as source of truth	17m 38s
RowNumber Fuzzer	15m 34s
Spark Bias Fuzzer	0s
Spark Fuzzer	15m 44s
Signature Changes	7s
	3h 39m 24s

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