feat: simplify key-valuer and adds 100% coverage

[rjfonseca]

Removes Stringer interface from the key-valuer interface.

Refactors with.go to remove an escaping param and better readability.

Adds 100% test coverage and fixes some minor issues when looping over
nil key-values.

[Copilot]

Pull Request Overview

This PR simplifies the KeyValuer interface by removing its String() method and refactors with.go for clearer function-name handling.

• Drops String() from KeyValuer and updates callers to use stringify.
• Introduces funcNameWithLineNumber helper and cleans up isAnonymousFunction.
• Updates formatter to call stringify(kv.Value()) instead of kv.String().

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
with.go	Extracted and optimized function-name-with-line helper; refactored anonymous check
kv.go	Removed String() from interface and internal stringer; switched to fmt.Stringer
formatter.go	Replaced kv.String() with stringify(kv.Value()) in output

Comments suppressed due to low confidence (2)

with.go:78

• The new helper funcNameWithLineNumber and the updated isAnonymousFunction logic aren’t covered by existing tests; consider adding unit tests to validate both normal and anonymous function name formatting.

func funcNameWithLineNumber(funcName string, line int) string {

with.go:68

• [nitpick] The comment describes only the dot-containing case but omits the behavior when no dot is found; consider updating it to fully explain both branches.

// It does this by checking if the function name contains a dot (.) and starts with "func" after the last dot.