explain: import into shows wrong number of request units consumed

**REPRO:**

1. Start the host:
`./cockroach start-single-node --insecure`

2. Create a tenant:
`./cockroach sql --insecure -e "SELECT crdb_internal.create_tenant(5);"`

3. Start the tenant:
`./cockroach mt start-sql --insecure --tenant-id=5 --sql-addr=:27000 --http-addr=:27001`

4. Create a table and insert 100K rows:
`./cockroach sql --insecure --url="postgresql://localhost:27000" -e "CREATE TABLE kv (k INT8 PRIMARY KEY, v BYTES); INSERT INTO kv (k, v) SELECT x, repeat('x', 1024)::bytes FROM generate_series(1,100000) g(x)"`

5. Export the table into a CSV:
`./cockroach sql --insecure --url="postgresql://localhost:27000" -e "SELECT * FROM kv" --format=csv > kv.csv`

6. Run a local HTTP server to serve the CSV:
`python3 -m http.server 3000`

7. Create a table to import into:
`./cockroach sql --insecure --url="postgresql://localhost:27000" -e "CREATE TABLE kv2 (k INT8 PRIMARY KEY, v BYTES)"`

8. `EXPLAIN ANALYZE` an import of the table:
`./cockroach sql --insecure --url="postgresql://localhost:27000" -e "EXPLAIN ANALYZE IMPORT INTO kv2 (k, v) CSV DATA ('http://localhost:3000/kv.csv')"`

**EXPECTED:**
The EXPLAIN output should show ~300K estimated RUs consumed.

**ACTUAL:**
The EXPLAIN output only shows ~42 estimated RUs consumed:
```
info
-----------------------------------
planning time: 61µs
execution time: 5.1s
distribution: local
vectorized: true
maximum memory usage: 10 KiB
network usage: 0 B (0 messages)
estimated RUs consumed: 42
isolation level: serializable
priority: normal
quality of service: regular

• import
nodes: n2
actual row count: 1
KV contention time: 0µs
(15 rows)
```

Jira issue: CRDB-33223