Please adapt fot Boost 1.90 or more recent

Hi,

I am trying to compile solarpowerlog on a recent system (Debian sid or Ubuntu 26.04) with Boost 1.90.

libboost-system-dev does not exist any longer and configure fails:

```
$ ./configure 
[...]
checking for the Boost system library... no
configure: error: cannot find flags to link with the Boost system library (libboost-system)
```
