How to resolve mutable borrow followed by immutable borrow within a loop in Rust?

I'm encountering a borrow checker issue in Rust where I am attempting to modify a Vec<u8> within a loop using splice, and then obtain a reference to the same Vec immediately afterwards. The error only occurs within the loop, as removing the loop resolves the issue. Below is the minimal code snippet that reproduces the error:

pub struct bz_stream_DState<'a> {
    pub next_in: Option<&'a [u8]>,
    pub state: *mut DState<'a>,
}

impl<'a> bz_stream_DState<'a> {
    pub fn set_next_in(&mut self, buf: &'a [u8]) {
        self.next_in = Some(buf);
    }
}

pub struct bzFile<'a> {
    pub buf_vec: Vec<u8>,
    pub strmD: bz_stream_DState<'a>,
}

pub struct DState<'a> {
    pub strm: *mut bz_stream_DState<'a>,
}

fn main() {
    let mut bzf = bzFile {
        buf_vec: vec![1, 2, 3, 4, 5],
        strmD: bz_stream_DState {
            next_in: None,
            state: std::ptr::null_mut(),
        },
    };

    for _i in 1..6 {
        let range = 0..1;
        let new_elements = [10, 11, 12];
        bzf.buf_vec.splice(range, new_elements.iter().cloned());
        let temp_buf_vec_ref = &bzf.buf_vec;
        bzf.strmD.set_next_in(temp_buf_vec_ref);
    }
}

The error message I receive is: (seen in rust playground)

error[E0502]: cannot borrow `bzf.buf_vec` as mutable because it is also borrowed as immutable
  --> src/main.rs:35:9
   |
35 |         bzf.buf_vec.splice(range, new_elements.iter().cloned());
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
...
39 |         let temp_buf_vec_ref = &bzf.buf_vec;
   |                                ------------
   |                                |
   |                                immutable borrow occurs here
   |                                immutable borrow later used here

The key point to note is that if I remove the for loop, the error does not occur. I've tried to separate the mutable and immutable borrows by introducing a new block scope within the loop, but it hasn't resolved the issue. Could someone help explain why the borrow checker is still not satisfied within the loop context and how to fix this error?

Additionally, if there are any improvements that could be made to the code structure to avoid such borrow checker issues, especially within loops, I would appreciate suggestions on that as well.

Context Background

I am trying to rewrite the original C code of bzip2 into Rust, notice the modification of bzf in the lines

Notice C code within while loop It first read

 n = fread ( bzf->buf, sizeof(UChar), 
                     BZ_MAX_UNUSED, bzf->handle );

Then we translated to Rust code to

 match handle.read(&mut bzf.buf_vec[total_read..]) {

using library below

impl Read for File {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.inner.read(buf)
    }

Then we use pub next_in: Option<&'a [u8]> to imitate the behavior of the array pointer in C