Implement Serialize/Deserialize for DATE, TIME, and DATETIME

[imurasawa]

Implement Serialize/Deserialize for DATE, TIME, and DATETIME

Problem

Current state of SerializeValue / DeserializeValue in Property.cs:

Type	Serialize (write)	Deserialize (read)
DATE	Falls through to default: ToString() — works	DateTime.Parse() — works
TIME	Falls through to default: ToString() — hundredths lost	DateTime.Parse() — works, but hundredths already lost
DATETIME	Falls through to default: ToString() — writes something, but…	No case → default: null → read returns null

Fix

Added explicit cases for DATE, TIME, and DATETIME in both SerializeValue and DeserializeValue, using the same ASCII format as bacnet-stack's datetime_to_ascii():

Type	Format
DATE	yyyy/MM/dd
TIME	HH:mm:ss.hh (hh = hundredths, 0–99)
DATETIME	yyyy/MM/dd-HH:mm:ss.hh

Note: C#'s DateTime does not have a hundredths field, so the conversion uses Millisecond / 10.

Verification

Read OBJECT_DATETIME_VALUE from a separate Linux machine (Raspberry Pi 4) using bacnet-stack's bacrp:

BACNET_IFACE=eth0 ./bacrp 22 44 1000 85
→ {Wednesday, May 27, 2026-17:47:33.95}

The value was correctly decoded on the bacnet-stack side.

Note: the display format produced by bacrp differs from yyyy/MM/dd-HH:mm:ss.hh; this is due to bacrp's own display formatting, not the wire encoding.

Notes

• Changed files: Storage/Property.cs only.
• No behaviour change for types other than DATE / TIME / DATETIME.
• Depends on Fix WritePropertyMultiple decoder to support multiple objects per request #158 (branch base). Can be reviewed independently; the datetime logic is self-contained.