Allows setting an explicit timestamp when generating a UUIDv7

[umeldt]

Providing the number of seconds since the UNIX epoch as the first argument to uuid7() creates a UUIDv7 from that timestamp instead of the default current time:

sqlite> .load dist/uuid
sqlite> select uuid7(0);
00000000-0000-7a9f-8e13-8c7852c6ea51
sqlite> select uuid7(1733668387);
0193a6b0-38b8-7762-9ca0-048beb946261

Not sure if this is too much of a niche use-case, but I've seem similar functionality in other libraries that implement UUIDv7.

[nalgeon]

Thanks!