change uniqueId

[cedryck1]

To fix the problem of notes from pdf not being created.

Example in pdf.lua file from Koreader :

["bookmarks"] = {
[1] = {
["page"] = 286,
["chapter"] = "12. Routines: Workout Programs",
["datetime"] = "2022-12-07 22:17:38",
["notes"] = "True brawn and power are developed by hard training sessions, not by long training sessions. Quality over quantity is an excellent motto for strength.",
["pos0"] = {
["page"] = 286,
["x"] = 113.53055169962,
["rotation"] = 0,
["y"] = 94.348024444745,
["zoom"] = 2.4036458333333,
},
["pos1"] = {
["page"] = 286,
["x"] = 355.4808284805,
["rotation"] = 0,
["y"] = 104.26570541035,
["zoom"] = 2.4036458333333,
},

pos0 and pos1 not always a string, using datetime instead for uniqueId.