Call `mp_event_handle_nowait()` in the VFS reader buffer refill path so
that pending scheduled events (USB task, network poll, etc.) get processed
during long-running import/parse/compile operations.
Without this, importing a large Python module from the filesystem blocks
for too long causing TinyUSB event queue to overflow. For example, on
renesas-ra, running a script that imports iperf3 via mpremote run, asserts,
most likely due to SOF interrupts not getting processing:
queue_event at lib/tinyusb/src/device/usbd.c:382
dcd_event_handler at lib/tinyusb/src/device/usbd.c:1318
dcd_event_sof at lib/tinyusb/src/device/dcd.h:237
dcd_int_handler at tinyusb/src/portable/renesas/rusb2/dcd_rusb2.c:964
<signal handler called>
disk_ioctl at extmod/vfs_fat_diskio.c:125
validate at lib/oofatfs/ff.c:3359
f_read at lib/oofatfs/ff.c:3625
file_obj_read at extmod/vfs_fat_file.c:75
mp_stream_rw at py/stream.c:60
mp_reader_vfs_readbyte at extmod/vfs_reader.c:59
next_char at py/lexer.c:174
mp_lexer_to_next at py/lexer.c:713
mp_parse at py/parse.c:1167
Signed-off-by: iabdalkader <i.abdalkader@gmail.com>
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