feature request：numeric and timestamp cs cast to bpchar cs

[amutu]

now it is not support:
postgres=# select cs_hash_count( cs_cast(ts,'bpchar') || stacktopsignature) from samp3_get();
ERROR: cast to timeseries of CHAR(N) is not supported
CONTEXT: PL/pgSQL function cs_cast(timeseries,cs_elem_type) line 3 at RETURN
Time: 0.485 ms
postgres=# select cs_hash_count( cs_cast(ts,'varchar') || stacktopsignature) from samp3_get();
ERROR: cast to timeseries of CHAR(N) is not supported
CONTEXT: PL/pgSQL function cs_cast(timeseries,cs_elem_type) line 3 at RETURN
Time: 0.338 ms

so,result like this is not fuser riendly：
postgres=# select s.cnt,s.grp from samp3_get(),cs_project(cs_hash_count( ts || stacktopsignature)) as s(cnt bigint,grp char(128)) order by 1 desc limit 10;
NOTICE: IMCS command: cat
NOTICE: IMCS command: hash_count
NOTICE: IMCS command: project
cnt | grp
-----+----------------
336 | \x1F)z\x0C\x01
129 |
112 |
112 | @\x0B\x17\x01
109 |
109 | &ʤ\x12\x01
108 | @\x0B\x17\x01
107 | \x16>\x11\x01
106 |
104 | &ʤ\x12\x01
(10 rows)

Time: 5777.381 ms

[amutu]

duplicate with #17