refactor(common): consolidate interval protobuf encode/decode logic

[xiangjinwu]

As with other PrimitiveArrayItemType, an interval value is encoded to and decoded from protobuf in the following:

risingwave/src/common/src/types/interval.rs

Lines 196 to 201 in 630685f

	pub fn to_protobuf<T: Write>(self, output: &mut T) -> ArrayResult<usize> {
	output.write_i32::<BigEndian>(self.months)?;
	output.write_i32::<BigEndian>(self.days)?;
	output.write_i64::<BigEndian>(self.ms)?;
	Ok(16)
	}

risingwave/proto/data.proto

Lines 111 to 117 in 630685f

	message Datum {
	// bool array/bitmap: one byte, 0 for false (null), non-zero for true (non-null)
	// integer, float, double: big-endianness
	// interval: encoded to (months, days, milliseconds), big-endianness
	// varchar: encoded accorded to encoding, currently only utf8 is supported.
	bytes body = 1;
	}

risingwave/src/common/src/array/column_proto_readers.rs

Lines 100 to 113 in 953e4b2

	pub fn read_interval_unit(cursor: &mut Cursor<&[u8]>) -> ArrayResult<IntervalUnit> {
	let mut read = || {
	let months = cursor.read_i32::<BigEndian>()?;
	let days = cursor.read_i32::<BigEndian>()?;
	let ms = cursor.read_i64::<BigEndian>()?;
	Ok::<_, std::io::Error>(IntervalUnit::new(months, days, ms))
	};
	match read() {
	Ok(iu) => Ok(iu),
	Err(e) => bail!("Failed to read IntervalUnit from buffer: {}", e),
	}
	}

However, as a special case, when it is part of HopWindow, there exists another code path:

risingwave/src/common/src/types/interval.rs

Lines 515 to 534 in 630685f

	#[expect(clippy::from_over_into)]
	impl Into<IntervalUnitProto> for IntervalUnit {
	fn into(self) -> IntervalUnitProto {
	IntervalUnitProto {
	months: self.months,
	days: self.days,
	ms: self.ms,
	}
	}
	}
	impl From<&'_ IntervalUnitProto> for IntervalUnit {
	fn from(p: &'_ IntervalUnitProto) -> Self {
	Self {
	months: p.months,
	days: p.days,
	ms: p.ms,
	}
	}
	}

risingwave/proto/data.proto

Lines 10 to 14 in 630685f

	message IntervalUnit {
	int32 months = 1;
	int32 days = 2;
	int64 ms = 3;
	}

It is better to consolidate them, although we do not foresee many future changes except #4514 and the maintenance cost of keeping them in sync may not be high.

[github-actions]

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