Bugfix chrono panic + hotifx PR15544 (#15549)

Closes  #13972

# Description
First commit: a hotfix concerning my last PR #15544! I had a
``unwrap_or_default`` that resulted in all years before ~1800 being
considered as "now", because the ``num_nanoseconds()`` overflowed.
Cc @fdncred 

Second: about #13972
Negative years are not allowed with RFC 2822 formatting, so I fallback
RTC 3339 in such cases.

If you want you might Rebase and Merge, and not squash.

# User-Facing Changes
On master 🔴 :
```nu
~> {year: 1900} | into datetime
Mon, 1 Jan 1900 00:00:00 +0200 (125 years ago)
# OK

~> {year: 1000} | into datetime
Wed, 1 Jan 1000 00:00:00 +0200 (now)
# NOT OK: now?

~> {year: -1000} | into datetime
-1000-01-01T00:00:00+02:00 (now)
# NOT OK: now?

~> {year: -1000} | into datetime | format date 
Error:   × Main thread panicked.
  ├─▶ at C:\Users\RIL1RT\.cargo\registry\src\index.crates.io-6f17d22bba15001f\chrono-0.4.39\src\datetime\mod.rs:626:14
  ╰─▶ writing rfc2822 datetime to string should never fail: Error
  help: set the `RUST_BACKTRACE=1` environment variable to display a backtrace.
# NOT OK: panics
```

On this branch 🟢 :
```nu
~> {year: 1900} | into datetime
Mon, 1 Jan 1900 00:00:00 +0200 (in 125 years)
~>  {year: 1000} | into datetime
Wed, 1 Jan 1000 00:00:00 +0200 (1025 years ago)
~> {year: -1000} | into datetime
-1000-01-01T00:00:00+02:00 (3025 years ago)
~> {year: -1000} | into datetime | format date
-1000-01-01T00:00:00+02:00
~> '3000 years ago' | date from-human | format date
-0975-04-11T18:18:24.301641100+02:00
```

# Tests + Formatting

# After Submitting
Nothing required IMO

crates/nu-protocol/src/value/mod.rs

@@ -4020,10 +4020,19 @@ fn operator_type_error(
 fn human_time_from_now(val: &DateTime<FixedOffset>) -> HumanTime {
     let now = Local::now().with_timezone(val.offset());
     let delta = *val - now;
-    let delta_seconds = delta.num_nanoseconds().unwrap_or(0) as f64 / 1_000_000_000.0;
-    let delta_seconds_rounded = delta_seconds.round() as i64;
-
-    HumanTime::from(Duration::seconds(delta_seconds_rounded))
+    match delta.num_nanoseconds() {
+        Some(num_nanoseconds) => {
+            let delta_seconds = num_nanoseconds as f64 / 1_000_000_000.0;
+            let delta_seconds_rounded = delta_seconds.round() as i64;
+            HumanTime::from(Duration::seconds(delta_seconds_rounded))
+        }
+        None => {
+            // Happens if the total number of nanoseconds exceeds what fits in an i64
+            // Note: not using delta.num_days() because it results is wrong for years before ~936: a extra year is added
+            let delta_years = val.year() - now.year();
+            HumanTime::from(Duration::days(delta_years as i64 * 365))
+        }
+    }
 }
 
 #[cfg(test)]