MeshRelation: precompute exclusion lookups outside the hot loop

[jmquigs]

isExcluded was called O(M*R) times from the nearest-neighbor loop. Each call rebuilt active-pattern closures, repeatedly uppercased the same strings, allocated "EXCLUDE." + refA / "INCLUDE." + refA, and even hit Logging.getLogOnceFn (dictionary lookup + string concat) on every iteration of every mod annotation.

Replace it with a one-time precompute that produces:

• refUncondExcl : bool[] (any annotation == "EXCLUDE")
• refGroups : HashSet[] (uppercased ref groups)
• modExcludeTokens / modIncludeTokens : string[][]
  (the X parts of Exclude.X /
  Include.X, uppercased)

The returned filter is now: O(|exclude tokens| + |include tokens|) per (modIdx, refIdx) pair, with HashSet.Contains lookups, no allocations, and no logging in the hot path. Diagnostic logOnce calls are fired once at precompute time per distinct token rather than per inner-loop hit.

Behavior is preserved:

• ref vert with "EXCLUDE" annotation -> excluded
• mod "Exclude.X" + ref has group "X" -> excluded
• mod "Include.X" + ref missing group "X" -> excluded
• empty AVG arrays (either side) -> filter is a no-op, matching the previous early-out
• out-of-range indices return false, matching the prior bounds checks