fix(tools): derive the amalgamation copyright year at generation time

Compute the end year of the copyright range when the amalgamation is
generated instead of hardcoding it, so it cannot go stale again. Honor
SOURCE_DATE_EPOCH so that reproducible builds still get a stable header.

tools/amalgamate.py

@@ -6,6 +6,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import argparse
+import datetime
 import os.path
 import re
 
@@ -25,6 +26,16 @@ if pos > 0:
 include_re = re.compile("^#[\\s]*include (\".*\").*$|^#[\\s]*include (<open62541/.*>).*$")
 guard_re = re.compile(r"^#(?:(?:ifndef|define)\s*[A-Z_]+_H_|endif /\* [A-Z_]+_H_ \*/|endif // [A-Z_]+_H_|endif\s*/\*\s*!?[A-Z_]+_H[_]+\s*\*/)")
 
+# End year of the copyright range. Honor SOURCE_DATE_EPOCH so that
+# reproducible builds get a stable header
+# (https://reproducible-builds.org/specs/source-date-epoch/).
+source_date_epoch = os.environ.get("SOURCE_DATE_EPOCH")
+if source_date_epoch:
+    copyright_year = datetime.datetime.fromtimestamp(
+        int(source_date_epoch), datetime.timezone.utc).year
+else:
+    copyright_year = datetime.date.today().year
+
 print ("Starting amalgamating file "+ args.outfile)
 
 file = open(args.outfile, 'w', encoding='utf8', errors='replace')
@@ -34,7 +45,7 @@ file.write("""/* THIS IS A SINGLE-FILE DISTRIBUTION CONCATENATED FROM THE OPEN62
  */
 
 /*
- * Copyright (C) 2014-2026 the open62541 contributors, as named in the
+ * Copyright (C) 2014-%d the open62541 contributors, as named in the
  * per-file copyright headers reproduced below
  *
  * This file is part of open62541. open62541 is free software: you can
@@ -44,7 +55,7 @@ file.write("""/* THIS IS A SINGLE-FILE DISTRIBUTION CONCATENATED FROM THE OPEN62
  * open62541 is distributed in the hope that it will be useful, but WITHOUT ANY
  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  * A PARTICULAR PURPOSE.
- */\n\n""" % args.version)
+ */\n\n""" % (args.version, copyright_year))
 
 if is_c:
     file.write('''#ifndef UA_DYNAMIC_LINKING_EXPORT