fix:timedot: parse unitful quantities more accurately (fix #2096)

A quantity with a unit like "15m" was being parsed internally as
0.249999999... rather than 0.25 (and since hledger 1.21, printed that
way also). Now we round such quantities to two places during parsing,
to get exact quarter-hour amounts.

hledger-lib/Hledger/Read/TimedotReader.hs

@@ -52,6 +52,7 @@ import Text.Megaparsec.Char
 import Hledger.Data
 import Hledger.Read.Common hiding (emptyorcommentlinep)
 import Hledger.Utils
+import Data.Decimal (roundTo)
 
 --- ** doctest setup
 -- $setup
@@ -228,7 +229,7 @@ numericquantityp = do
   let q' =
         case msymbol of
           Nothing  -> q
-          Just sym ->
+          Just sym -> roundTo 2 $
             case lookup sym timeUnits of
               Just mult -> q * mult
               Nothing   -> q  -- shouldn't happen.. ignore

hledger/test/timedot.test

@@ -42,3 +42,18 @@ $ hledger -ftimedot:- reg
 # 3. Tags are recognised. Account aliases are applied.
 $ hledger -ftimedot:- reg tag:posting-tag --alias fos:haskell=λ
 2023-01-01 different transac..  (λ)                           1.00          1.00
+
+# 4. Each of these formats is printed as exactly a quarter hour.
+<
+2023-01-01
+a  .
+b  0.25
+c  15m
+
+$ hledger -ftimedot:- print
+2023-01-01 *
+    (a)            0.25
+    (b)            0.25
+    (c)            0.25
+
+>=