Allow fractional skill counts

[unrealdreamz]

Summary

Fixes #1708.

Allows decimal values in skill Count fields so users can model partial uptime / average-use contributions through the existing Full DPS count scalar.

Root Cause

The Full DPS calculation path already multiplies by numeric count values, and XML save/load already serializes them with tonumber / tostring. The practical blockers were the UI and text paths:

• skill count edit boxes filtered out decimal points,
• pasted/copied skill groups only accepted integer counts,
• Full DPS labels only showed counts when count >= 2, hiding values like 0.5x even though the DPS was scaled.

Fix

• Allow decimal input for group and gem Count fields.
• Preserve decimal counts in copy/paste skill-group text.
• Keep invalid/empty count input falling back to 1.
• Show any non-1 Full DPS count in labels/export, including values below 1.
• Update the count tooltip from "integer" to "numeric".
• Add a regression proving pasted 0.5 count is preserved and halves Full DPS.

Validation

Local, non-GUI validation only:

gh pr list --repo PathOfBuildingCommunity/PathOfBuilding-PoE2 --state open -S "1708 fractional skill count" -> []
git diff --check -> passed
git diff --cached --check -> passed
git show --check --stat --oneline HEAD -> passed
where.exe lua -> not found
where.exe luajit -> not found
where.exe busted -> not found

I did not run Busted locally because this Windows checkout does not have Lua/LuaJIT/Busted on PATH. I also avoided Docker/GUI validation so no visible command windows or heavy processes were launched.

Risk / Rollback

Low-to-moderate risk. This does not change Full DPS semantics; it only lets decimal counts reach the existing scalar and makes the display honest. Rollback is this commit.