fix(codegen): map postgres range columns to PgRange for oxide format

[Mattt (aevv)]

Range columns generate a struct that compiles and then fails to decode. sea-schema surfaces them as ColumnType::Custom, which write_rs_type renders as String — correct for the standard format, where get_col_type_attrs pairs it with select_as = "text", but the oxide format decodes straight into the model struct via sqlx::FromRow:

ColumnDecode { index: "range", source: "mismatched types; Rust type
  `Option<String>` (as SQL type `TEXT`) is not compatible with SQL type `NUMRANGE`" }

This is latent rather than live: bin_table_data.bin_range has been an int8range generating as Option<String> for a while, but oxide never hits it because ev_db hand-writes its own BinTableData with Option<PgRange<i64>> — plausibly because the generated one was unusable. This PR makes the generated type match that hand-written one, so the workaround can eventually go away.

All six range types now render as sqlx's PgRange, honouring --date-time-crate for the temporal ones.

Two constraints shape the output:

• PgRange implements neither Serialize nor Deserialize, and serde has no impls for std::ops::Bound, so there is nothing to derive. Range fields carry #[serde(skip)]; skipping needs Default to deserialize, so they are always Option regardless of nullability. This matches existing practice — the hand-written BinTableData derives no serde at all — but it does mean a range is silently absent from JSON rather than failing loudly. If a consumer ever needs it serialized, the fix is to emit a representation here rather than to un-skip.
• BigDecimal implements only PartialEq, so an entity holding a numrange cannot derive Eq. get_oxide_eq_needed handles that the way get_eq_needed already does for floats. Ranges over Eq element types keep the derive.

Verified by regenerating evervault/common-specs against a live Postgres and reading a real numrange row back into the generated struct.

The three pre-existing sea-orm-codegen --lib failures (test_get_info, test_get_rs_type_with_chrono, test_gen_postgres) are the Json mapping ones already noted in #24, unrelated to this change.

🤖 Generated with Claude Code