[error] Remove redundant Error wrappers + Add RuntimeError type + Replace DecimoError with specific error types (#198)

This PR refactors Decimo’s error-handling to raise the library’s typed
`DecimoError[...]` aliases directly (e.g., `ValueError`,
`OverflowError`) instead of wrapping them in `Error(...)`, introduces a
`RuntimeError` type, and updates call sites/tests accordingly.

**Changes:**
- Remove redundant `Error(...)` wrappers across TOML parsing, numeric
parsing, and arithmetic modules.
- Add `RuntimeError` as a `DecimoError[...]` alias and update
runtime-infrastructure failure sites (e.g., MPFR
availability/allocation).
- Replace uses of the generic `DecimoError` wrapper with more specific
error types (and update tests to match).

Author: forfudan

docs/plans/gmp_integration.md

@@ -1321,7 +1321,7 @@ LD_LIBRARY_PATH=./src/decimo/gmp ./myprogram
 
 ```bash
 bash src/decimo/gmp/build_gmp_wrapper.sh \
-&& mojo build -I src \
+&& pixi run mojo build -I src \
     -Xlinker -L./src/decimo/gmp -Xlinker -ldecimo_gmp_wrapper \
     -o /tmp/myprogram myprogram.mojo \
 && DYLD_LIBRARY_PATH=./src/decimo/gmp /tmp/myprogram

src/decimo/bigdecimal/arithmetics.mojo

@@ -320,11 +320,9 @@ def true_divide(
     """
     # Check for division by zero
     if y.coefficient.is_zero():
-        raise Error(
-            ZeroDivisionError(
-                message="Division by zero.",
-                function="true_divide()",
-            )
+        raise ZeroDivisionError(
+            message="Division by zero.",
+            function="true_divide()",
         )
 
     # Handle dividend of zero
@@ -698,11 +696,9 @@ def true_divide_inexact(
 
     # Check for division by zero
     if x2.coefficient.is_zero():
-        raise Error(
-            ZeroDivisionError(
-                message="Division by zero.",
-                function="true_divide_inexact()",
-            )
+        raise ZeroDivisionError(
+            message="Division by zero.",
+            function="true_divide_inexact()",
         )
 
     # Handle dividend of zero
@@ -916,11 +912,9 @@ def truncate_divide(x1: BigDecimal, x2: BigDecimal) raises -> BigDecimal:
     """
     # Check for division by zero
     if x2.coefficient.is_zero():
-        raise Error(
-            ZeroDivisionError(
-                message="Division by zero.",
-                function="truncate_divide()",
-            )
+        raise ZeroDivisionError(
+            message="Division by zero.",
+            function="truncate_divide()",
         )
 
     # Handle dividend of zero
@@ -961,11 +955,9 @@ def truncate_modulo(
     """
     # Check for division by zero
     if x2.coefficient.is_zero():
-        raise Error(
-            ZeroDivisionError(
-                message="Division by zero.",
-                function="truncate_modulo()",
-            )
+        raise ZeroDivisionError(
+            message="Division by zero.",
+            function="truncate_modulo()",
         )
 
     return subtract(

src/decimo/bigdecimal/bigdecimal.mojo

@@ -27,7 +27,7 @@ from std.memory import UnsafePointer
 from std.python import PythonObject
 from std import testing
 
-from decimo.errors import DecimoError, ConversionError, ValueError
+from decimo.errors import ConversionError, ValueError
 from decimo.rounding_mode import RoundingMode
 from decimo.bigdecimal.rounding import round_to_precision
 from decimo.bigint10.bigint10 import BigInt10
@@ -362,22 +362,18 @@ struct BigDecimal(
             return Self(coefficient=BigUInt.zero(), scale=0, sign=False)
 
         if value != value:  # Check for NaN
-            raise Error(
-                ValueError(
-                    message="Cannot convert NaN to BigDecimal.",
-                    function="BigDecimal.from_scalar()",
-                )
+            raise ValueError(
+                message="Cannot convert NaN to BigDecimal.",
+                function="BigDecimal.from_scalar()",
             )
         # Convert to string with full precision
         try:
             return Self.from_string(String(value))
         except e:
-            raise Error(
-                ConversionError(
-                    message="Cannot convert scalar to BigDecimal.",
-                    function="BigDecimal.from_scalar()",
-                    previous_error=e^,
-                )
+            raise ConversionError(
+                message="Cannot convert scalar to BigDecimal.",
+                function="BigDecimal.from_scalar()",
+                previous_error=e^,
             )
 
     @staticmethod
@@ -544,12 +540,10 @@ struct BigDecimal(
             return Self(coefficient=coefficient^, scale=scale, sign=sign)
 
         except e:
-            raise Error(
-                ConversionError(
-                    message="Failed to convert Python Decimal to BigDecimal.",
-                    function="BigDecimal.from_python_decimal()",
-                    previous_error=e^,
-                ),
+            raise ConversionError(
+                message="Failed to convert Python Decimal to BigDecimal.",
+                function="BigDecimal.from_python_decimal()",
+                previous_error=e^,
             )
 
     # ===------------------------------------------------------------------=== #

src/decimo/bigdecimal/constants.mojo

@@ -165,10 +165,8 @@ def pi(precision: Int) raises -> BigDecimal:
     """
 
     if precision < 0:
-        raise Error(
-            ValueError(
-                message="Precision must be non-negative", function="pi()"
-            )
+        raise ValueError(
+            message="Precision must be non-negative", function="pi()"
         )
 
     # TODO: When global variables are supported,