fix: lower requires-python to >=3.10 and sync pyproject.toml version to 0.4.0

Add `from __future__ import annotations` to all modules missing it
(_http.py, _xml.py, exceptions.py, _mappings.py) so PEP 604 union
syntax works on Python 3.10+.

Author: jsulopzs

pyproject.toml

@@ -1,19 +1,22 @@
 [project]
 name = "python-entsoe"
-version = "0.3.0"
+version = "0.4.0"
 description = "Python client for the ENTSO-E Transparency Platform API"
 readme = "README.md"
 license = "MIT"
 authors = [
     { name = "jsulopzs", email = "jesus.lopez@datons.com" },
 ]
-requires-python = ">=3.13"
+requires-python = ">=3.10"
 keywords = ["entsoe", "energy", "electricity", "api", "transparency"]
 classifiers = [
     "Development Status :: 3 - Alpha",
     "Intended Audience :: Science/Research",
     "License :: OSI Approved :: MIT License",
     "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
+    "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Topic :: Scientific/Engineering",
 ]

src/entsoe/_http.py

@@ -7,6 +7,8 @@
 - Response validation
 """
 
+from __future__ import annotations
+
 import io
 import logging
 import time

src/entsoe/_mappings.py

@@ -1,5 +1,7 @@
 """ENTSO-E area codes, document types, and PSR type mappings."""
 
+from __future__ import annotations
+
 # Country code (ISO 3166-1 alpha-2) → ENTSO-E EIC area code
 AREA_CODES: dict[str, str] = {
     "AL": "10YAL-KESH-----5",

src/entsoe/_xml.py

@@ -10,6 +10,8 @@
 All share the TimeSeries > Period > Point structure.
 """
 
+from __future__ import annotations
+
 import re
 import xml.etree.ElementTree as ET
 from datetime import timedelta

src/entsoe/exceptions.py

@@ -1,5 +1,7 @@
 """Exception hierarchy for the ENTSO-E client."""
 
+from __future__ import annotations
+
 
 class ENTSOEError(Exception):
     """Base exception for all ENTSO-E API errors."""