log : add CONT level for continuing previous log entry

[ggerganov]

ref #9418 (comment)

Useful to print things on the same line as the previous log message which might have a prefix (e.g. timestamp, level, etc.). For example:

            LOG_INF("%s: static prompt based on n_keep: '", __func__);
            for (int i = 0; i < params.n_keep; i++) {
                LOG_CNT("%s", llama_token_to_piece(ctx, embd_inp[i]).c_str());
            }
            LOG_CNT("'\n");

0.00.815.053 I    198 -> '
'
0.00.815.053 I main: static prompt based on n_keep: '<|im_start|>system
You are'
0.00.815.060 I 
0.00.815.062 I main: interactive mode on.

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