Fix Trino transpilation of nullable single field ROW generated from EXCLUDE

[alancai98]

Issue #, if available:

• Resolves Trino transpilation failing for union(string, null) #44

Description of changes:

• For background, PartiQL structs are represented by a ROW type. When there is just one field within the ROW type, then we must know the type when constructing the ROW.

-- in PartiQL, a struct with single field `a` of type `int4`
struct(a: int4)

-- in Trino, a row with a single field `a` of type `int4`
CAST(ROW(a) AS ROW(a INTEGER))

• The bug mentioned in Trino transpilation failing for union(string, null) #44 comes from when we transpile EXCLUDE and there is a ROW with a single field
• Adds logic to handle the construction of a single field ROW when the field's type is a union(<some single type>, null). New logic will remove the null from the union since Trino types are nullable by default.
  • Note: this behavior will be fixed w/ the next PLK release, 0.15+, due to Deprecates absent types and removes associated planner logic partiql-lang-kotlin#1463.

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