Replace standard json library by segmentio's library

[dcu]

The segmentio json library is a drop-in replacement that it's faster than the standard library. In this case it's ~37% faster.

goos: darwin
goarch: arm64
pkg: github.com/aws/aws-lambda-go/lambda
       │ bench.orig.txt │           bench.json.txt            │
       │     sec/op     │   sec/op     vs base                │
JSON-8      7.901µ ± 0%   4.985µ ± 0%  -36.90% (p=0.000 n=40)

       │ bench.orig.txt │             bench.json.txt             │
       │      B/op      │     B/op       vs base                 │
JSON-8     4.353Ki ± 0%   38.273Ki ± 0%  +779.34% (p=0.000 n=40)

       │ bench.orig.txt │       bench.json.txt       │
       │   allocs/op    │ allocs/op   vs base        │
JSON-8       31.00 ± 0%   17.00 ± 0%  -45.16% (n=40)

re #381

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c4e28da) 72.63% compared to head (c58d997) 72.63%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #527   +/-   ##
=======================================
  Coverage   72.63%   72.63%           
=======================================
  Files          26       26           
  Lines        1407     1407           
=======================================
  Hits         1022     1022           
  Misses        314      314           
  Partials       71       71           

Files	Coverage Δ
cfn/response.go	69.44% <ø> (ø)
cfn/wrap.go	66.66% <ø> (ø)
events/attributevalue.go	78.46% <ø> (ø)
events/cloudwatch_logs.go	60.00% <ø> (ø)
events/codebuild.go	40.90% <ø> (ø)
events/duration.go	40.00% <ø> (ø)
events/ecs_container_instance.go	81.25% <ø> (ø)
events/epoch_time.go	72.72% <ø> (ø)
events/kafka.go	81.25% <ø> (ø)
events/lambda_function_urls.go	79.41% <ø> (ø)
... and 5 more

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[bmoffatt]

I'm not comfortable expanding the dependencies of aws-lambda-go beyond that of Go's standard library.