jsontext: fix Decoder.Reset to preserve internal buffer capacity

[fpetkovski]

The Decoder.Reset method is not preserving the internal buffer between resets, causing buffer capacity to be lost and resulting in unnecessary allocations when reusing decoders. This is particularly problematic when decoding many small messages.

This commit fixes the Reset method to preserve the internal buffer. It makes sure aliasing is removed if the buffer currently points to an internal byte slice of a bytes.Buffer. It adds a TestDecoderReset test structured into subtests to better validate the different scenarios.

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Patch Set 1:

(1 comment)

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