Gravity generator sound overhaul (#86080)

## About The Pull Request
<details>
<summary>Video comparisons</summary>


https://github.com/user-attachments/assets/0dc6d936-6c43-4696-9488-ced2a6f63cd2


https://github.com/user-attachments/assets/17072a5f-3254-40a1-bfaa-216b7613ece5

<details>
<summary>OUTDATED</summary>


https://github.com/user-attachments/assets/6ec5393c-63cf-4d05-9b53-a6a925090c96

</details>
</details>
<br>
</details>
Took me a long time

## Why It's Good For The Game

Previous sound was very grating on the ears so we made a more light one.

## Changelog
🆑 grungussuss and kayozz
sound: gravity generator has a new sound
/🆑

code/datums/looping_sounds/machinery_sounds.dm

@@ -126,10 +126,17 @@
 	falloff_distance = 1 //Instant falloff after initial tile
 
 /datum/looping_sound/gravgen
-	mid_sounds = list('sound/machines/gravgen/gravgen_mid1.ogg' = 1, 'sound/machines/gravgen/gravgen_mid2.ogg' = 1, 'sound/machines/gravgen/gravgen_mid3.ogg' = 1, 'sound/machines/gravgen/gravgen_mid4.ogg' = 1)
-	mid_length = 1.8 SECONDS
-	extra_range = 10
-	volume = 20
+	start_sound = 'sound/machines/gravgen/grav_gen_start.ogg'
+	start_length = 1 SECONDS
+	mid_sounds = list(
+		'sound/machines/gravgen/grav_gen_mid1.ogg' = 12,
+		'sound/machines/gravgen/grav_gen_mid2.ogg' = 1,
+	)
+	mid_length = 1.1 SECONDS
+	end_sound = 'sound/machines/gravgen/grav_gen_end.ogg'
+	extra_range = 8
+	vary = TRUE
+	volume = 70
 	falloff_distance = 5
 	falloff_exponent = 20