🐛 Fix scientific notation in QASM import (cda-tum#560)

## Description

This PR fixes a small bug in the QASM importer that would prevent it
from properly importing floating point numbers in scientific notation.

## Checklist:

<!---
This checklist serves as a reminder of a couple of things that ensure
your pull request will be merged swiftly.
-->

- [x] The pull request only contains commits that are related to it.
- [x] I have added appropriate tests and documentation.
- [x] I have made sure that all CI jobs on GitHub pass.
- [x] The pull request introduces no new warnings and follows the
project's style guidelines.

---------

Signed-off-by: burgholzer <[email protected]>

src/parsers/qasm3_parser/Scanner.cpp

@@ -1,6 +1,12 @@
 #include "parsers/qasm3_parser/Scanner.hpp"
 
+#include <cstdint>
+#include <istream>
+#include <optional>
 #include <regex>
+#include <sstream>
+#include <stdexcept>
+#include <string>
 
 namespace qasm3 {
 char Scanner::readUtf8Codepoint(std::istream* in) {
@@ -186,12 +192,26 @@ Token Scanner::consumeNumberLiteral() {
       error("Float literals are only allowed in base 10");
     }
 
-    char const sep = ch;
-    nextCh();
-    auto valAfterDecimalSeparator = consumeNumberLiteral(base);
+    std::stringstream ss{};
+    ss << valBeforeDecimalSeparator;
+
+    if (ch == '.') {
+      ss << ch;
+      nextCh();
+      const auto valAfterDecimalSeparator = consumeNumberLiteral(base);
+      ss << valAfterDecimalSeparator;
+    }
 
-    std::stringstream ss;
-    ss << valBeforeDecimalSeparator << sep << valAfterDecimalSeparator;
+    if (ch == 'e' || ch == 'E') {
+      ss << ch;
+      nextCh();
+      if (ch == '+' || ch == '-') {
+        ss << ch;
+        nextCh();
+      }
+      const auto valAfterExponent = consumeNumberLiteral(base);
+      ss << valAfterExponent;
+    }
 
     try {
       t.valReal = std::stod(ss.str());

test/unittests/test_qasm3_parser.cpp

@@ -743,14 +743,16 @@ TEST_F(Qasm3ParserTest, ImportQasm3CPrefix) {
 TEST_F(Qasm3ParserTest, ImportQasmScanner) {
   std::stringstream ss{};
   const std::string testfile =
-      "$1 : . .5 -1. -= += ++ *= **= ** /= % %= |= || | &= "
+      "$1 : . .5 -1. 1.25e-3 1e3 -= += ++ *= **= ** /= % %= |= || | &= "
       "&& & ^= ^ ~= ~ ! <= <<= << < >= >>= >> >";
   const auto tokens = std::vector{
       qasm3::Token::Kind::HardwareQubit,
       qasm3::Token::Kind::Colon,
       qasm3::Token::Kind::Dot,
       qasm3::Token::Kind::FloatLiteral,
       qasm3::Token::Kind::FloatLiteral,
+      qasm3::Token::Kind::FloatLiteral,
+      qasm3::Token::Kind::FloatLiteral,
       qasm3::Token::Kind::MinusEquals,
       qasm3::Token::Kind::PlusEquals,
       qasm3::Token::Kind::DoublePlus,