Improve TableScan with filters pushdown unparsing (multiple filters)

[sgrebnov]

Which issue does this PR close?

With filters pushdown optimization, the LogicalPlan can have filters defined as part of TableScan and Filter nodes.
To avoid overwriting one of the filters, we combine the existing filter with the additional filter.

Example query

select
        c_phone as cntrycode,
        c_acctbal
from
        customer
where c_mktsegment = 'BUILDING' and c_acctbal > (
        select
                avg(c_acctbal)
        from
                customer);

Logical Plan

|  Projection: customer.c_phone AS cntrycode, customer.c_acctbal                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   Filter: CAST(customer.c_acctbal AS Decimal128(38, 6)) > (<subquery>)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
|     Subquery:
|     ..                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|     TableScan: customer, full_filters=[customer.c_mktsegment = Utf8("BUILDING")]

W/o this change it will be unparsed as

select
        c_phone as cntrycode,
        c_acctbal
from
        customer
where c_mktsegment = 'BUILDING'

What changes are included in this PR?

Improves QueryBuilder pub fn selection to combine filters if select is called multiple times (select corresponds to query filter / WHERE clause).

Are these changes tested?

Added unit test, tested as part of TPC-H and TPC-DS queries unparsing by https://github.com/spiceai/spiceai (running benchmarks with some filters pushdown optimizations enabled)

Are there any user-facing changes?

Fixes some unparsing issues related to missing WHERE clauses when running TPC-H and TPC-DS queries with filters pushdown optimization enabled

[goldmedal]

Thanks @sgrebnov it looks good to me 👍