chore: refactor formatter and value functions

[rjfonseca]

Refactor the Value functions and the formatter to fix an error with the formatter when the key was not a string.

The Value* functions were refactored to be more consistent. Now Value* returnas always the first occurrence and Values* returns all occurrences of a key.

Now the formatter will print all the keys in the reverse order of creation (most recent first).

Other formatters were added for convenience.

[Copilot]

Pull Request Overview

This PR refactors how key-value pairs are retrieved and formatted in errors, fixes a formatter error when keys aren’t strings, and adds convenience formatters.

• Extracted and unified Value*/Values* helpers into value.go to consistently return most recent or all occurrences.
• Revised formatter logic in formatter.go to use ValueAllSlice with new write* helpers and introduced RootErrorFormatter and RootErrorKVFormater.
• Updated KV constructor and stringify in kv.go and adjusted tests in formatter_test.go for multi-type values.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
value.go	New dedicated file for Value/Values/Map helpers
kv.go	Adjusted KV constructor and improved stringify
formatter.go	Refactored main formatter, added helper writers & new formatters
formatter_test.go	Test updated for mixed-type key-value formatting
error.go	Removed duplicate retrieval functions, streamlined Error
error_test.go	Removed empty test file

Comments suppressed due to low confidence (2)

formatter.go:8

• The comment refers to FullFormatter but the actual function and constant are named FullFormater (one ‘t’). Update the comment to match the code or rename the function for consistency.

// DefaultFormatter is the default formatter used when no custom formatter is set.

formatter.go:46

• The function name FullFormater (and similarly RootErrorKVFormater) is misspelled—‘Formatter’ is typically spelled with two ‘t’s. Consider renaming to FullFormatter for clarity.

func FullFormater(err error) string {