Whitespaces inside the quotation changes the behavior of `TZ="TIMEZONE"`

Start in src/items/timezone.rs and review the existing TZ="..." parser and its current tests. Check the whitespace cases described in the issue, then verify that the parser accepts the proposed inner whitespace behavior without changing unrelated timezone forms; done means the relevant tests pass with the intended offsets.

This was a minor comment on https://github.com/uutils/parse_datetime/pull/232#issuecomment-3421283917 and it was suggested to create a separate issue for it

The following is the original copied here:

Hello, thanks to everybody for the great work.

I was studying this PR for a while and I was wondering that is there any reason (beyond performance) on why TZ="VALUE" is not relaxed with inner optional whitespaces (i.e TZ=" VALUE ")? Since such change passes all the current tests, this is a bit confusing to me.

This changes some behavior in an example like the following:

// prefixed whitespace
test(r#"TZ=" UTC-5:20:15""#, fixed_offset(0)); // current
test(r#"TZ=" UTC-5:20:15""#, fixed_offset(19215)); // with relaxed conditions

// prefixed whitespace
test(r#"TZ="UTC-5:20:15 ""#, Err(Backtrack(ContextError { context: [], cause: None }))); // current
test(r#"TZ="UTC-5:20:15 ""#, fixed_offset(19215)); // with relaxed conditions

Naturally, this can be generalized to the cases with :.

Whitespace relaxation can further improve in an unrelated example like: parse_datetime(" TZ=\"...\""). However in parse_datetime example, the user can easily just trim the input while removing the inner spaces of the quotation of this case is not as simple so that's why I think it's a quality improvement (if it is justified to begin with).

Example of changes that will relax this limitation:

diff --git a/src/items/timezone.rs b/src/items/timezone.rs
index 0414ee8..0009d17 100644
--- a/src/items/timezone.rs
+++ b/src/items/timezone.rs
@@ -16,6 +16,7 @@

 use jiff::tz::{Offset, TimeZone};
 use winnow::{
+    ascii::space0,
     combinator::{alt, delimited, opt, preceded, repeat},
     stream::AsChar,
     token::{one_of, take_while},
@@ -25,7 +26,12 @@ use winnow::{
 use super::primitive::{dec_uint, plus_or_minus};

 pub(super) fn parse(input: &mut &str) -> ModalResult<TimeZone> {
-    delimited("TZ=\"", preceded(opt(':'), alt((posix, iana))), '"').parse_next(input)
+    delimited(
+        ("TZ=\"", space0),
+        preceded(opt((':', space0)), alt((posix, iana))),
+        (space0, "\""),
+    )
+    .parse_next(input)
 }

 /// Parse a posix (proleptic) timezone string (e.g., "UTC7", "JST-9").