Replace librange's position scan with ClassicAPI's UnitInRange

librange was a per-frame position scanner: it swept party/raid unit
tokens, cached each one's distance via UnitPosition, and answered range
queries from that cache. All of it existed only because 1.12 had no cheap
way to check an arbitrary unit's distance. ClassicAPI's UnitInRange does
exactly that C-side (fixed 40y healing range, position miss reported via
the second return), so the whole library collapses to a direct call.

Wins from dropping the cache:
- No staleness. The scanner's zone-death and roster-reindex bugs simply
  can't exist without a cache to go stale, so this supersedes the
  keep-alive fixes from 756e8840.
- All classes get target-frame range fading. The old target path faked a
  40y check via IsActionInRange on a healing spell found on the action
  bar, so classes without such a spell (GetRangeSlot returned nil) never
  had a working target range check.

The rangecheck == "0" master switch used to be enforced by hiding the
scanner; with no scanner, move that gate into pfUI.api.UnitInRange so
disabling the check still means nothing fades. Threshold is now 40y (the
ClassicAPI constant) rather than the old 45y. Drop the now-dead
rangechecki (Range Check Interval) setting, its GUI row, and migration.

api/api.lua

@@ -143,6 +143,11 @@ function pfUI.api.UnitInRange(unit)
     return 1
   end
 
+  -- master switch: with the 40y check off, a visible unit beyond interact
+  -- range counts as in range (nothing fades). Invisible units already
+  -- returned nil above, matching the pre-collapse behavior.
+  if C.unitframes.rangecheck == "0" then return 1 end
+
   -- UnitXP precise mode: skip librange entirely, use direct distance check
   if C.unitframes.rangecheck_mode == "unitxp" and _G.UnitXP then
     local threshold = tonumber(C.unitframes.rangecheck_distance) or 40

api/config.lua

@@ -232,7 +232,6 @@ function pfUI:LoadConfig()
   pfUI:UpdateConfig("unitframes", nil,           "druidmanaspace",   "-3")
   pfUI:UpdateConfig("unitframes", nil,           "druidmanatexture", "Interface\\AddOns\\pfUI\\img\\bar")
 
-  pfUI:UpdateConfig("unitframes", nil,           "rangechecki",      "4")
   pfUI:UpdateConfig("unitframes", nil,           "combowidth",       "6")
   pfUI:UpdateConfig("unitframes", nil,           "comboheight",      "6")
   pfUI:UpdateConfig("unitframes", nil,           "swingtimerwidth",  "200")
@@ -1110,13 +1109,6 @@ function pfUI:MigrateConfig()
     end
   end
 
-  -- migrating rangecheck interval (> 3.2.2)
-  if checkversion(3, 2, 2) then
-    if tonumber(pfUI_config.unitframes.rangechecki) <= 1 then
-      pfUI_config.unitframes.rangechecki = "2"
-    end
-  end
-
   -- migrating legacy buff/debuff naming (> 3.5.0)
   if checkversion(3, 5, 0) then
     local unitframes = { "player", "target", "focus", "group", "grouptarget", "grouppet", "raid", "ttarget", "pet", "ptarget", "fallback" }