fix(ray_trace): don't bail out of blockAtEntityCursor when yaw or pitch is 0

[Xuxchloris]

Fixes #3935.

Problem

blockAtEntityCursor() validated entity.yaw / entity.pitch with truthiness checks, so a legitimate orientation of exactly 0 (facing -Z, or looking level) was treated as missing and the ray trace was skipped — the function returned null even though the entity orientation was valid.

Change

lib/plugins/ray_trace.js: use null checks (entity.pitch == null || entity.yaw == null) so 0 is a valid angle while truly missing values still short-circuit.

Tests

Added to test/internalTest.js (run across all tested versions):

• yaw === 0 (facing -Z) returns the block in front.
• pitch === 0 (facing +X) returns the block in front.
• Missing yaw/pitch still returns null.

Verification

• mocha test/internalTest.js --grep blockAtEntityCursor — 81/81 passing (3 tests × 27 supported versions).
• standard lint clean.

[Xuxchloris]

Heads-up on the failing "MC 1.21.8 1.21.9 1.21.11" job (I can't view its logs without admin rights, so here's the evidence I have):

• The new blockAtEntityCursor internal tests pass locally on all 27 supported versions (81/81), and the full internalTest suite for 1.21.8 / 1.21.9 / 1.21.11 passes too (72 passing, 3 skipped).
• This exact job is also failing on unrelated open PRs in this repo (e.g. 🎈 26.2 #3926 and 26.x: attack packet, use_entity shape, clockUpdates time, player_loaded #3958), which points to the same pre-existing external-test flakiness already seen on fix: recompute dig waitTime after lookAt so dig speed matches server state (fixes #3910) #3961's "MC 1.21.3–1.21.6" job rather than a regression from this PR.
• I also hardened the test's geometry (3-block gold columns instead of single blocks) so small eye-height variations can't push the ray onto a voxel boundary.

Could you re-run the job? Happy to dig further if it still fails.

[Xuxchloris]

Update: the updated commit (e128c15) now passes all 11 checks — the earlier "MC 1.21.8 1.21.9 1.21.11" failure did not reproduce. No rerun needed. 👍