Fix group by month in non-ms precision and mixed unit

bug1: group by month are not correct in non-ms time precision;

repeat steps:

• config time_precision as `ns` 
• insert into root.test(time,s1) values (1,1)
• select count(s1) from root.test group by ([2023-01-01, 2027-01-01), 1mo)

analytic & design doc: https://apache-iotdb.feishu.cn/docx/TNBPd8nZUoDsJMxjdOncOUkcnVA#Q8MhdMrGmolJsCxLCljcuPtznRh

bug2: group by month are not correct when use mixed unit time duration.

repeat steps:

• insert into root.test(time,s1) values (1,1)
• select count(s1) from root.test group by ([2023-01-01, 2027-01-01), 1mo1d1s)