Complete the DamageEvent migration: one deal() entry point for every attacker

The bull's Hitbox already routed through DamageEvent, but the spear, the bear's
maul, and the matador's reach-gore still did raw Object.call(&"take_sword_hit", ...)
— the exact scattered string paths DamageEvent was meant to retire. Add a single
static DamageEvent.deal(target, cause, at, source, knock_up) that builds the typed
event and hands it to receive_damage(), falling back to the legacy string call for
any not-yet-migrated victim, and route all four attackers (Hitbox included) through
it. The damage_pipeline characterization test proves the bull's outcomes are
unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq1VX2o1ZfiNRdCjD294wf

matador.gd

@@ -955,7 +955,7 @@ func _try_melee_hit(reach: float) -> void:
 	if facing.dot(to_bull / dist) < cos(deg_to_rad(DP.f("mat_stab_arc"))):
 		return
 	_blade_hit_cd = DP.f("mat_stab_cooldown")
-	_bull.call(&"take_sword_hit", "gored")
+	DamageEvent.deal(_bull, DamageEvent.Cause.GORED, _bull.global_position, self)
 
 
 func _enter_ragdoll(hit_dir: Vector3, bull_speed: float, up_boost: float = 0.0) -> void: