DataError messages leak the literal {...} placeholder (missing f-string prefix) #1372

Two DataError messages in the pure-Python implementation are plain string literals that contain {...} placeholders but are missing the f prefix, so the literal placeholder text is shown to the user instead of the offending value.

1. psycopg/types/datetime.py:692 — _get_timestamp_load_error():

return DataError("timestamp too small (before year 1): {s!r}")

The two sibling branches immediately below it are correctly f-strings (f"timestamp too large (after year 10K): {s!r}", f"can't parse timestamp {s!r}: ..."), which is what makes the missing prefix stand out.

2. psycopg/types/json.py:280 — JsonbBinaryLoader.load():

raise DataError("unknown jsonb binary format: {data[0]}")

Reproduction (pure-Python, no server needed)

from psycopg.types.datetime import _get_timestamp_load_error
from psycopg.types.json import JsonbBinaryLoader
from psycopg import _oids

print(_get_timestamp_load_error(None, b"0001-01-01 00:00:00 BC"))
# -> timestamp too small (before year 1): {s!r}

try:
    JsonbBinaryLoader(_oids.JSONB_OID, None).load(b"\x02{}")
except Exception as e:
    print(e)
# -> unknown jsonb binary format: {data[0]}

Expected

timestamp too small (before year 1): '0001-01-01 00:00:00 BC'
unknown jsonb binary format: 2

A repo-wide grep confirms these are the only two occurrences of the pattern (every other {...}-in-a-plain-string case is an intentional sql.SQL(...).format(...) template). I'll open a PR adding the missing f prefix to both.