fix: reset INI decoder state on init

[xieby1]

Generated by Hermes + GPT-5.5.

Summary

• Reset the INI decoder's finished flag in Init
• Add a regression test covering decoder reuse across multiple inputs

Context

eval-all reuses the same decoder instance for each input file. The INI decoder set finished = true after decoding the first input, but did not reset it in Init, so subsequent files were treated as EOF immediately.

This caused commands such as:

yq ea -p ini -o yaml '{"fi": fileIndex, "fn": filename, "doc": .}' a.ini b.ini

to only process a.ini.

Test Plan

GOPROXY=https://goproxy.cn,direct go test ./pkg/yqlib -run "TestINIDecoderInitResetsFinished|TestINIScenarios"

Also manually verified:

go run . ea -p ini -o yaml '{"fi": fileIndex, "fn": filename, "doc": .}' a.ini b.ini

now outputs both fileIndex: 0 and fileIndex: 1.