bearing: fix final bearing returning values outside [-180, 180]

[JSap0914]

Summary

bearing(start, end, { final: true }) can return values in the range (180, 360) instead of the documented [-180, 180].

Root cause

calculateFinalBearing reverses the point pair and adds 180° to get the final bearing:

let bear = bearing(end, start); // in [-180, 180]
bear = (bear + 180) % 360;      // yields [0, 360) — wrong when bear > 0
return bear;

When bearing(end, start) returns a positive value (e.g. 90°), the result is 270° — outside the documented range and inconsistent with every other bearing API in Turf.

Fix

Add a single normalisation step after the modulo:

return bear > 180 ? bear - 360 : bear;

Concrete example

// Traveling due west along the equator
bearing(point([10, 0]), point([0, 0]), { final: true })
// before: 270   ← wrong
// after:  -90   ← correct

Changes

• packages/turf-bearing/index.ts: one-line normalisation in calculateFinalBearing
• packages/turf-bearing/test.ts: new test case covering the westward edge case
• packages/turf-helpers/README.md: auto-regenerated by the pre-commit hook (not related to this fix)

Resolves the documented contract that bearing() returns values between -180 and 180 degrees.

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