refactor: migrate to the official yaml package

[andreynering]

• Closes gopkg.in/yaml.v3 is unmaintained, consider migrating to https://github.com/yaml/go-yaml #2171

The old package is long archived, but the YAML org forked it and will officially maintain it from now on.

• Old: https://github.com/go-yaml/yaml
• New: https://github.com/yaml/go-yaml

[Copilot]

Pull Request Overview

This PR migrates from the archived gopkg.in/yaml.v3 package to the officially maintained go.yaml.in/yaml/v4 package. The YAML organization has forked the old package and will maintain it going forward.

• Updates all YAML package imports across the codebase from v3 to v4
• Updates the go.mod file to use the new package dependency
• Refactors error handling code to work with the new YAML package's error structure

Reviewed Changes

Copilot reviewed 24 out of 25 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
go.mod	Updates dependency from gopkg.in/yaml.v3 to go.yaml.in/yaml/v4
taskrc/reader.go	Updates YAML import to new package
taskfile/reader.go	Updates YAML import to new package
taskfile/ast/*.go	Updates YAML imports across all AST files
internal/templater/funcs.go	Updates YAML import to new package
errors/error_taskfile_decode.go	Updates YAML import and refactors error handling for new package

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