Form-Data: Boundary string not cut off completely 🐛
**Describe the bug** 🐛
The auto-generated boundary string is not cut off completely from the request body string when I use  
```
parseFormData(req.body)
```
**To Reproduce** 👨‍🔬
Steps to reproduce the behavior:
1. create file to send to the server, e.g. example.txt with the following content: "some input file, e.g. a certificate"
2. implement a post route using happyx
3. send the file using a multipart/form-data body ( I use postman to send the request)
4. On the server side, parse the request body with the happyx function parseFormData(req.body)
5. print the parsed form data or write it to a file
6. observe the file

**Expected output** 🤔
console output or file content: 
```
"some input file, e.g. a certificate"
```
**Actual output**
```
"some input file, e.g. a certificate"
----------------------
```
**Additional info**
The complete boundary string generated by postman is the following:
```
----------------------------196777003309965867532698
```
So apparently happy x does cut off something, but not the whole boundary string.

 - OS: FreeBSD 13.1
 - Nim compiler 2.0
 - HappyX: head
 - Project type: ssr
 - HTTP Server default


**Edit:** I realized that the two trailing dashes after the boundary string of the last form-data element mark the end of the whole multi-part form data, so I removed it from the initial question. The main problem, as explained above, remains, though.