ucode: update to Git HEAD (2025-12-01)

ucode: update to Git HEAD (2025-12-01)

afe4be60628a lib/fs: fix return value for flush
5f08ecf8e372 lib/uloop: fix return value doc for run()
1affe484f302 lib/uloop: pass eof and error to cb
559860cbd76d lib: introduce io library
ef07e2448a56 vm: optimize string+string concat with ucv_string_alloc

Changes: https://github.com/jow-/ucode/compare/48ed18d2532e9197212c34473ab926c7b5e8ac73...f7c2b97a82e8b505bf4b2c0d8883b5116e1960f9

Backport PR to fix compilation with Ubuntu 18.04:
https://github.com/jow-/ucode/pull/355

Link: https://github.com/openwrt/openwrt/pull/21100
Signed-off-by: Hauke Mehrtens <[email protected]>
(cherry picked from commit e40ca676eee20fa6ea8b5ac36b3a858481ed9d79)