[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/ncruces/julianday/julianday.go

@@ -0,0 +1,124 @@
+// Package julianday provides Time to Julian day conversions.
+package julianday
+
+import (
+	"bytes"
+	"errors"
+	"math"
+	"strconv"
+	"time"
+)
+
+const secs_per_day = 86_400
+const nsec_per_sec = 1_000_000_000
+const nsec_per_day = nsec_per_sec * secs_per_day
+const epoch_days = 2_440_587
+const epoch_secs = secs_per_day / 2
+
+func jd(t time.Time) (day, nsec int64) {
+	sec := t.Unix()
+	// guaranteed not to overflow
+	day, sec = sec/secs_per_day+epoch_days, sec%secs_per_day+epoch_secs
+	return day, sec*nsec_per_sec + int64(t.Nanosecond())
+}
+
+// Date returns the Julian day number for t,
+// and the nanosecond offset within that day,
+// in the range [0, 86399999999999].
+func Date(t time.Time) (day, nsec int64) {
+	day, nsec = jd(t)
+	switch {
+	case nsec < 0:
+		day -= 1
+		nsec += nsec_per_day
+	case nsec >= nsec_per_day:
+		day += 1
+		nsec -= nsec_per_day
+	}
+	return day, nsec
+}
+
+// Float returns the Julian date for t as a float64.
+//
+// In the XXI century, this has submillisecond precision.
+func Float(t time.Time) float64 {
+	day, nsec := jd(t)
+	// converting day and nsec to float64 is exact
+	return float64(day) + float64(nsec)/nsec_per_day
+}
+
+// Format returns the Julian date for t as a string.
+//
+// This has nanosecond precision.
+func Format(t time.Time) string {
+	var buf [32]byte
+	return string(AppendFormat(buf[:0], t))
+}
+
+// AppendFormat is like Format but appends the textual representation to dst
+// and returns the extended buffer.
+func AppendFormat(dst []byte, t time.Time) []byte {
+	day, nsec := Date(t)
+	if day < 0 && nsec != 0 {
+		dst = append(dst, '-')
+		day = ^day
+		nsec = nsec_per_day - nsec
+	}
+	var buf [20]byte
+	dst = strconv.AppendInt(dst, day, 10)
+	frac := strconv.AppendFloat(buf[:0], float64(nsec)/nsec_per_day, 'f', 15, 64)
+	return append(dst, bytes.TrimRight(frac[1:], ".0")...)
+}
+
+// Time returns the UTC Time corresponding to the Julian day number
+// and nanosecond offset within that day.
+// Not all day values have a corresponding time value.
+func Time(day, nsec int64) time.Time {
+	return time.Unix((day-epoch_days)*secs_per_day-epoch_secs, nsec).UTC()
+}
+
+// FloatTime returns the UTC Time corresponding to a Julian date.
+// Not all date values have a corresponding time value.
+//
+// In the XXI century, this has submillisecond precision.
+func FloatTime(date float64) time.Time {
+	day, frac := math.Modf(date)
+	nsec := math.Floor(frac * nsec_per_day)
+	return Time(int64(day), int64(nsec))
+}
+
+// Parse parses a formatted Julian date and returns the UTC Time it represents.
+//
+// This has nanosecond precision.
+func Parse(s string) (time.Time, error) {
+	digits := 0
+	dot := len(s)
+	for i, b := range []byte(s) {
+		if '0' <= b && b <= '9' {
+			digits++
+			continue
+		}
+		if b == '.' && i < dot {
+			dot = i
+			continue
+		}
+		if (b == '+' || b == '-') && i == 0 {
+			continue
+		}
+		return time.Time{}, errors.New("julianday: invalid syntax")
+	}
+	if digits == 0 {
+		return time.Time{}, errors.New("julianday: invalid syntax")
+	}
+
+	day, err := strconv.ParseInt(s[:dot], 10, 64)
+	if err != nil && dot > 0 {
+		return time.Time{}, errors.New("julianday: value out of range")
+	}
+	frac, _ := strconv.ParseFloat(s[dot:], 64)
+	nsec := int64(math.Round(frac * nsec_per_day))
+	if s[0] == '-' {
+		nsec = -nsec
+	}
+	return Time(day, nsec), nil
+}