GPUParticles2D trail disappears instantly ignoring scale curve

### Tested versions

- Reproducible in: Godot v4.5.1, Godot v4.5, Godot v4.4

### System information

Godot v4.5.1.stable.mono - Windows 10 (build 19045) - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3050 Laptop GPU (NVIDIA; 31.0.15.3770) - AMD Ryzen 5 6600H with Radeon Graphics (12 threads) - 15.19 GiB memory

### Issue description

GPUParticles2D's trails disappear instantly when their lifetime ends and there seems to be no way to customize that. They ignore Scale Curve and Color Ramp.

https://github.com/user-attachments/assets/ae85b582-3adb-4a01-9d5c-cc9edf3036f4

### Steps to reproduce

I attached a minimal reproduction project.

### Minimal reproduction project (MRP)

[particle-trail-bug.zip](https://github.com/user-attachments/files/23362741/particle-trail-bug.zip)

Start by opening the attached particle-trail-bug.zip minimal reproduction project and reproducing the GPUParticles2D trail behavior in the listed Godot versions. Trace the GPUParticles2D trail lifetime handling and its Scale Curve and Color Ramp inputs; done means trails do not disappear instantly and those controls affect their ending behavior.

Written by the indexing model from the issue text.