fix(middleware/tracing): replace strings.TrimLeft with strings.CutPrefix for correct fullMethod parsing

[1911860538]

Replaced strings.TrimLeft with strings.CutPrefix to correctly handle fullMethod input.
strings.CutPrefix not only removes the leading '/', but also allows us to check whether fullMethod starts with a '/'.
This ensures that only the correct prefix is removed and provides a clear indication when the input doesn't follow the expected /package.service/method format.

[Copilot]

Pull Request Overview

This PR refines the parsing of gRPC fullMethod strings by using strings.CutPrefix instead of strings.TrimLeft, enabling detection of invalid formats and ensuring only a leading slash is removed.

• Use strings.CutPrefix to remove exactly one leading / and detect when it’s missing
• Introduce an early return with an attribute for inputs not following /package.service/method
• Keep downstream splitting logic unchanged

Comments suppressed due to low confidence (2)

middleware/tracing/span.go:105

• [nitpick] The boolean variable cut is ambiguous. Consider renaming it to something like hasPrefix or removedPrefix to clarify its purpose.

	name, cut := strings.CutPrefix(fullMethod, "/")

middleware/tracing/span.go:106

• The new branch handling inputs without a leading slash should be covered by unit tests to ensure correct behavior when fullMethod doesn't start with /.

	if !cut {