SR bitstream file header can attempt to read/write inconsistent data sizes

The split rendering bitstream header can read or write an inconsistent data size depending on compiler settings and platform.

The reason for this is the use of sizeof() with enum types, specifically ISAR_SPLIT_REND_CODEC and ISAR_SPLIT_REND_POSE_CORRECTION_MODE in split_rend_{reader,writer}_open().

c.f.:

• https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/blob/main/lib_util/split_render_file_read_write.c?ref_type=heads#L107
• https://forge.3gpp.org/rep/ivas-codec-pc/ivas-codec/-/blob/main/lib_util/split_render_file_read_write.c?ref_type=heads#L200

Instead of using sizeof( ENUM_TYPE ) the reads/writes should use sizeof( int32_t ) or something else consistent.