refactor: Replace c_longlong with i64 for consistency

For clarity and consistency, use explicit i64 instead of c_longlong.
While c_longlong is 64-bit on all platforms, i64 is clearer and
follows the same pattern as the previous commit that removed c_long.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: cfsmp3

src/rust/src/libccxr_exports/demuxer.rs

@@ -9,7 +9,7 @@ use lib_ccxr::common::{Codec, Options, StreamMode, StreamType};
 use lib_ccxr::time::Timestamp;
 use std::alloc::{alloc_zeroed, Layout};
 use std::ffi::CStr;
-use std::os::raw::{c_char, c_int, c_longlong, c_uchar, c_uint, c_void};
+use std::os::raw::{c_char, c_int, c_uchar, c_uint, c_void};
 
 // External C function declarations
 extern "C" {
@@ -452,12 +452,12 @@ pub unsafe extern "C" fn ccxr_demuxer_open(ctx: *mut ccx_demuxer, file: *const c
 /// # Safety
 /// This function is unsafe because it dereferences a raw pointer.
 #[no_mangle]
-pub unsafe extern "C" fn ccxr_demuxer_get_file_size(ctx: *mut ccx_demuxer) -> c_longlong {
+pub unsafe extern "C" fn ccxr_demuxer_get_file_size(ctx: *mut ccx_demuxer) -> i64 {
     if ctx.is_null() {
         return -1;
     }
     let mut demux_ctx = copy_demuxer_from_c_to_rust(ctx);
-    demux_ctx.get_filesize() as c_longlong
+    demux_ctx.get_filesize() as i64
 }
 
 // Extern function for ccx_demuxer_print_cfg