Fix CPR NL() off-by-one at the 87 deg polar boundary

[willi-werner]

Fixes an off-by-one in L0Latitude.NL() at exactly |lat| = 87.0 deg.

Problem

The topmost transition latitude T_LAT[57] rounds to exactly 87.0 deg and binarySearch matched it inclusively, so NL() returned 2 at |lat| = 87.0 deg, where the DO-260B standard (and the NASA/cpr formally-verified reference) require NL = 1 (polar cap). This changes longitude decoding for positions landing exactly on the 87 deg lattice point.

Fix

Treat the top transition latitude as exclusive for the NL=2 zone:

if (abslat >= T_LAT[T_LAT.length - 1]) return 1;   // |lat| >= 87 deg -> polar cap

Only the topmost boundary changes (it is the only NL transition latitude landing exactly on an exact integer-lattice point); the other 57 already matched NASA at every lattice point.

Validation

• New regression test cpr/L0LatitudeTest.java: NL==1 at +/-87/88.5/90 deg, NL==2 just below 87 deg, NL==59 at the equator.
• Full suite: 164 tests pass, 0 failures.
• Cross-checked against the NASA/cpr DO-260B reference: NL boundaries agree to ~2 cm; an exhaustive lattice check around all 58 NL boundaries now matches; a 1,000,000-position airborne+surface decode cross-check against NASA agrees to ~5 mm.
• Independently validated with GPT-5.5 (Codex).

Commit: 08b5ec6