Merge bitcoin/bitcoin#23156: refactor: Remove unused ParsePrechecks and ParseDouble

fa9d72a794 Remove unused ParseDouble and ParsePrechecks (MarcoFalke)
fa3cd28535 refactor: Remove unused ParsePrechecks from ParseIntegral (MarcoFalke)

Pull request description:

  All of the `ParsePrechecks` are already done by `ToIntegral`, so remove them from `ParseIntegral`.

  Also:
  * Remove redundant `{}`. See https://github.com/bitcoin/bitcoin/pull/20457#discussion_r720116866
  * Add missing failing c-string test case
  * Add missing failing test cases for non-int32_t integral types

ACKs for top commit:
  laanwj:
    Code review ACK fa9d72a794, good find on ParseDouble not being used at all, and testing for behavior of embedded NULL characters is always a good thing.
  practicalswift:
    cr ACK fa9d72a794

Tree-SHA512: 3d654dcaebbf312dd57e54241f9aa6d35b1d1d213c37e4c6b8b9a69bcbe8267a397474a8b86b57740fbdd8e3d03b4cdb6a189a9eb8e05cd38035dab195410aa7

src/util/strencodings.h

@@ -123,7 +123,9 @@ constexpr inline bool IsSpace(char c) noexcept {
 }
 
 /**
- * Convert string to integral type T.
+ * Convert string to integral type T. Leading whitespace, a leading +, or any
+ * trailing character fail the parsing. The required format expressed as regex
+ * is `-?[0-9]+`.
  *
  * @returns std::nullopt if the entire string could not be parsed, or if the
  *   parsed value is not in the range representable by the type T.
@@ -137,7 +139,7 @@ std::optional<T> ToIntegral(const std::string& str)
     if (first_nonmatching != str.data() + str.size() || error_condition != std::errc{}) {
         return std::nullopt;
     }
-    return {result};
+    return result;
 }
 
 /**
@@ -182,13 +184,6 @@ std::optional<T> ToIntegral(const std::string& str)
  */
 [[nodiscard]] bool ParseUInt64(const std::string& str, uint64_t *out);
 
-/**
- * Convert string to double with strict parse error feedback.
- * @returns true if the entire string could be parsed as valid double,
- *   false if not the entire string could be parsed or when overflow or underflow occurred.
- */
-[[nodiscard]] bool ParseDouble(const std::string& str, double *out);
-
 /**
  * Convert a span of bytes to a lower-case hexadecimal string.
  */