Add parser support for nested select functions

[absurdfarce]

Expand on functionality described in #137 to support something like the following as well:

SELECT toTimestamp(now()) FROM system.local

Even with the changes in #137 I'm seeing the following error for this query:

Exception in thread "main" com.datastax.oss.driver.api.core.servererrors.InvalidQueryException: unexpected argument type for function call 'toTimestamp(...)' in select statement

toTimestamp() is something of a canary here. Broadly speaking there's probably room to talk about most of the parser selectors as a general "function" with a lookup table for specific outputs (or something similar). For now I'm just trying to get the idea of this usage as an entry point for thinking about this type of nesting.

[absurdfarce]

Hmmm, now that's kinda interesting:

$ ccm node1 cqlsh 127.0.0.1 9142
Connected to cql-proxy at 127.0.0.1:9142
[cqlsh 6.0.0 | Cassandra 4.0.2 | CQL spec 3.4.5 | Native protocol v4]
Use HELP for help.
cqlsh> select now() from system.local;

 system.now()
--------------------------------------
 3baaf89b-0a85-11f0-a12e-5ea5e7761742

(1 rows)

2025-03-26T15:59:39.647-0500	DEBUG   proxy/proxy.go:672  	Query handled by proxy  {"query": "select now() from system.local;", "stream": 3}

So far so good... that all seems right.

$ ccm node1 cqlsh 127.0.0.1 9142
Connected to cql-proxy at 127.0.0.1:9142
[cqlsh 6.0.0 | Cassandra 4.0.2 | CQL spec 3.4.5 | Native protocol v4]
Use HELP for help.
cqlsh> select toTimestamp('3baaf89b-0a85-11f0-a12e-5ea5e7761742') from system.local;
InvalidRequest: Error from server: code=2200 [Invalid query] message="unexpected argument type for function call 'toTimestamp(...)' in select statement"
cqlsh> select toTimestamp("3baaf89b-0a85-11f0-a12e-5ea5e7761742") from system.local;
InvalidRequest: Error from server: code=2200 [Invalid query] message="unsupported function call 'toTimestamp' in select statement"

2025-03-26T16:03:56.211-0500	DEBUG   proxy/proxy.go:672  	Query handled by proxy  {"query": "select toTimestamp('3baaf89b-0a85-11f0-a12e-5ea5e7761742') from system.local;", "stream": 3}
2025-03-26T16:03:56.211-0500	ERROR   proxy/proxy.go:674  	error parsing query to see if it's handled  	{"error": "unexpected argument type for function call 'toTimestamp(...)' in select statement"}
github.com/datastax/cql-proxy/proxy.(*client).handleQuery
    	/work/git/cql-proxy/proxy/proxy.go:674
github.com/datastax/cql-proxy/proxy.(*client).Receive
    	/work/git/cql-proxy/proxy/proxy.go:580
github.com/datastax/cql-proxy/proxycore.(*Conn).read
    	/work/git/cql-proxy/proxycore/conn.go:114
2025-03-26T16:04:14.368-0500	DEBUG   proxy/proxy.go:672  	Query handled by proxy  {"query": "select toTimestamp(\"3baaf89b-0a85-11f0-a12e-5ea5e7761742\") from system.local;", "stream": 4}
2025-03-26T16:04:14.368-0500	ERROR   proxy/proxy.go:674  	error parsing query to see if it's handled  	{"error": "unsupported function call 'toTimestamp' in select statement"}
github.com/datastax/cql-proxy/proxy.(*client).handleQuery
    	/work/git/cql-proxy/proxy/proxy.go:674
github.com/datastax/cql-proxy/proxy.(*client).Receive
    	/work/git/cql-proxy/proxy/proxy.go:580
github.com/datastax/cql-proxy/proxycore.(*Conn).read
    	/work/git/cql-proxy/proxycore/conn.go:114

[absurdfarce]

For reference, this against Cassandra 4.0.2:

Connected to cass-402-1 at 127.0.0.1:9042
[cqlsh 6.0.0 | Cassandra 4.0.2 | CQL spec 3.4.5 | Native protocol v5]
Use HELP for help.
cqlsh> select now() from system.local;

 system.now()
--------------------------------------
 eb740cb0-0acd-11f0-8b89-37f677328a52

(1 rows)
cqlsh> select toTimestamp(now()) from system.local; 

 system.totimestamp(system.now())
----------------------------------
  2025-03-27 05:40:07.990000+0000

(1 rows)