Cube SQL pg_type returns NULL instead of 0 for typsend/typoutput

# Bug Report: Cube SQL pg_type returns NULL instead of 0 for typsend/typoutput

## Summary

Postgrex/Ecto fails to connect to Cube SQL API because `pg_type` system catalog returns NULL for `typsend` and `typoutput` columns instead of 0.

## Error

```
** (ArgumentError) errors were found at the given arguments:
* 1st argument: not a binary
(stdlib) :binary.copy(nil)
(postgrex 0.21.1) lib/postgrex/types.ex:137: Postgrex.Types.build_type_info/1
(postgrex 0.21.1) lib/postgrex/protocol.ex:1092: Postgrex.Protocol.bootstrap_recv/4
(postgrex 0.21.1) lib/postgrex/protocol.ex:749: Postgrex.Protocol.handshake/3
(postgrex 0.21.1) lib/postgrex/protocol.ex:229: Postgrex.Protocol.connect_endpoints/6
```

## Root Cause

Postgrex type bootstrap queries `pg_type` to get type send/receive functions. The query expects `typsend` and `typoutput` to be OIDs (integers), but Cube returns NULL for these columns.

### Postgrex Bootstrap Query

```sql
SELECT t.oid, t.typname, t.typsend, t.typreceive, t.typoutput, t.typinput,
t.typelem, t.typbasetype, t.typnamespace, t.typdelim, COALESCE(c.reltype, 0),
COALESCE(r.rngsubtype, 0), t.typtype, t.typcategory
FROM pg_type AS t
LEFT JOIN pg_class AS c ON c.oid = t.typrelid
LEFT JOIN pg_range AS r ON r.rngtypid = t.oid
```

## Reproduction

### Query to verify the issue

```sql
SELECT t.oid, t.typname,
t.typsend IS NULL as typsend_null,
t.typoutput IS NULL as typoutput_null,
t.typreceive IS NULL as typreceive_null
FROM pg_type AS t
LIMIT 5;
```

### Current Cube Output (BROKEN)

```
oid | typname | typsend_null | typoutput_null | typreceive_null
-----+---------+--------------+----------------+-----------------
16 | bool | t | t | f
17 | bytea | t | t | f
19 | name | t | t | f
20 | int8 | t | t | f
21 | int2 | t | t | f
```

Note: `typsend` and `typoutput` are NULL (`t`), but `typreceive` correctly returns non-NULL (`f`).

### Expected Output (PostgreSQL behavior)

```
oid | typname | typsend | typoutput | typreceive
-----+---------+---------+-----------+------------
16 | bool | 2436 | 16 | 2436
17 | bytea | 2412 | 31 | 2412
19 | name | 2422 | 359 | 2422
20 | int8 | 2408 | 461 | 2408
21 | int2 | 2404 | 39 | 2404
```

All columns should return either a valid OID or 0, never NULL.

## Suggested Fix

In Cube's `pg_type` implementation, return `0` instead of `NULL` for:
- `typsend`
- `typoutput`

This is consistent with how `typreceive` already returns 0 or a valid OID.

## Affected Software

- Postgrex 0.19+ (Elixir PostgreSQL driver)
- Ecto.Adapters.Postgres (Elixir ORM)
- Any PostgreSQL client that queries `pg_type` for type metadata during connection bootstrap

## Environment

- Cube SQL API via PostgreSQL wire protocol (port 15432)
- Postgrex 0.21.1
- Ecto 3.13.x
- Elixir 1.18.3
- Erlang/OTP 27

## Related

This blocks using Ecto with Cube SQL API for querying cubes via standard PostgreSQL protocol.