Configure default timezone

[lziq]

Issue #410

Solution Description:

We want to provide an option to configure default timezone offset through EvaluationSession class, since the default timezone offset should be considered as a kind of information provided when we evaluate the time.

Changes Details:

Source code:

1. Added the new attribute defaultTimezoneOffset to EvaluationSession class. The default value is set to be UTC time.
2. Removed the global field DEFAULT_TIMEZONE_OFFSET.
3. Modified the source code for time evaluation and time cast, so that the default timezone is now provided by EvaluationSession.

Test:

1. Added test for defaultTimezoneOffset for EvaluationSession class.
2. Added test for time evaluation.
3. Added test for time cast.
4. Created a local variable defaultTimezoneOffset to replace DEFAULT_TIMEZONE_OFFSET for test cases using it.

[codecov-commenter]

Codecov Report

Merging #449 (b7ee8bf) into main (6301396) will increase coverage by 0.00%.
The diff coverage is 88.88%.

@@            Coverage Diff            @@
##               main     #449   +/-   ##
=========================================
  Coverage     82.35%   82.36%           
- Complexity     1394     1395    +1     
=========================================
  Files           171      171           
  Lines         10717    10722    +5     
  Branches       1766     1766           
=========================================
+ Hits           8826     8831    +5     
  Misses         1350     1350           
  Partials        541      541           

Flag	Coverage Δ
CLI	18.18% <ø> (ø)
EXAMPLES	74.85% <ø> (ø)
LANG	84.86% <88.88%> (+<0.01%)	⬆️
PTS	∅ <ø> (∅)
TEST_SCRIPT	79.68% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ng/src/org/partiql/lang/eval/EvaluatingCompiler.kt	84.22% <ø> (ø)
...g/src/org/partiql/lang/eval/ExprValueExtensions.kt	84.71% <50.00%> (ø)
...ang/src/org/partiql/lang/eval/EvaluationSession.kt	100.00% <100.00%> (ø)

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[dlurton]

Mostly looks good to me, just one minor change requested. Thanks.

[alancai98]

Only had a few minor comments. Looks good overall!

[abhikuhikar]

EvaluationSession class also has a now: Timestamp member. It can have its own time zone offset defined. I was wondering if it would conflict with a separate default time zone. Should we consider using now.localOffset which is time zone offset in minutes? (It can be null though). Need to investigate more into this.

For the PR, just one minor suggestion. Otherwise looks great to me.

[alancai98]

Nice job