Remove need to supply PostgresDecodingContext on decode

[fabianfett]

Motivation

To use a customized JSONDecoder, users have the option to supply a PostgresDecodingContext. Currently we require users to set explicitly on every row decode call. This makes the API unnecessarily verbose. Since the PostgresDecodingContext is generic we can not default the parameter. Instead we need add proxy functions so that we can default the parameter manually.

Changes

• Add decode methods omitting the PostgresDecodingContext

[codecov-commenter]

Codecov Report

Merging #307 (17ba80f) into main (17ba80f) will not change coverage.
The diff coverage is n/a.

❗ Current head 17ba80f differs from pull request most recent head a2affaf. Consider uploading reports for the commit a2affaf to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #307   +/-   ##
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  Coverage   43.94%   43.94%           
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  Files         115      115           
  Lines        9670     9670           
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  Hits         4249     4249           
  Misses       5421     5421           

Flag	Coverage Δ
unittests	43.94% <0.00%> (ø)

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[gwynne]

LGTM

[fabianfett]

The API breakage detector reports a false positive here. The decode methods have been moved from PostgresRowSequence to extension AsyncSequence where Element == PostgresRow, which PostgresRowSequence conforms to.