Replace deprecated strings.Title() in scheduler metrics

[dejanzele]

Is your feature request related to a problem? Please describe.

strings.Title() is deprecated since Go 1.18 and we still use it in two places in the scheduler metrics code.

Describe the solution you'd like

Replace both calls with cases.Title(language.English).String(...) from golang.org/x/text/cases and golang.org/x/text/language.

Files to change

• internal/scheduler/metrics.go:484 - strings.Title(strings.ToLower(phase))
• internal/scheduler/metrics.go:493 - strings.Title(strings.ToLower(phase))

Example

// Before
phase: strings.Title(strings.ToLower(phase)),

// After
phase: cases.Title(language.English).String(strings.ToLower(phase)),

The cases.Title caser is safe for concurrent use, so you can create it once as a package-level variable rather than creating a new one on every call.

Acceptance criteria

• Both strings.Title() calls replaced
• No strings.Title import remains
• go test ./internal/scheduler/... passes
• golangci-lint run ./internal/scheduler/... passes