iis: fix collector panic on application pool names containing '#'

[Copilot]

deduplicateIISNames panicked with slice bounds out of range whenever any IIS application pool name contained a # character, because the function assumed # only appears as a perflib counter suffix (Site_B#2).

Bugs fixed

In deduplicateIISNames (iis.go):

• strings.Split(name, "#")[0] misidentified "App#Pool" as a duplicate of "App" — replaced with iisCounterBaseName() that validates the suffix is purely numeric via strconv.Atoi
• Inverted if/else: code that should record a new entry was instead writing to originalIndex (zero value 0), corrupting the first element
• slices.Delete(counterValues, index, 1) used 1 as the end index rather than index+1, causing the panic
• Function returned nothing — callers never saw the deduplicated slice; now returns []T
• Lexicographic sort meant "Site_B#9" incorrectly superseded "Site_B#10"; algorithm now tracks the winning numeric suffix with integer comparison

In iis_w3svc_w3wp.go:

• strings.Contains(name, "#") skipped metrics for any pool whose name legitimately contains #; replaced with iisCounterBaseName() stripping so only real perflib numeric suffixes are normalised

New helper

// iisCounterBaseName strips a trailing "#<digits>" suffix only.
// "Site_B#2"  → "Site_B"
// "App#Pool"  → "App#Pool"   (non-numeric: unchanged)
// "Pool#Name#2" → "Pool#Name"
func iisCounterBaseName(name string) string { … }

All five callers updated to assign the returned slice. Unit tests added for both iisCounterBaseName and deduplicateIISNames.

• Fixes IIS Collector Panic Caused by Certain Characters in Application Names #2472