Create default values for union during copying / runtime

[05st]

In Value::createDefaultValue we were initializing a union value with a single null value as the default child. This resulted in the child lacking required information when copying from certain types. For example, childrenSize of the child would be 0, and so if the selected field turned out to be a struct (with more than one field), none of its fields would be copied, resulting in an empty output. E.g.

return union_value(a := struct_pack(b := 2))
{}

when the correct output should be {b: 2}

The solution implemented here was to just set up default union values with no children, and create the default child value during copying once we know the selected field.

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.94%. Comparing base (34b1eb7) to head (5da8b0d).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/common/types/value/value.cpp	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5772      +/-   ##
==========================================
- Coverage   85.94%   85.94%   -0.01%     
==========================================
  Files        1620     1620              
  Lines       73512    73510       -2     
  Branches     8788     8783       -5     
==========================================
- Hits        63181    63179       -2     
  Misses      10107    10107              
  Partials      224      224              

Flag	Coverage Δ
extension	63.36% <87.50%> (+<0.01%)	⬆️
in-mem	81.67% <87.50%> (-0.01%)	⬇️
on-disk	86.53% <87.50%> (-0.01%)	⬇️
recovery	86.53% <87.50%> (-0.01%)	⬇️

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[github-actions]

Benchmark Result

Master commit hash: 309be4327d91ca8213873c907d8d3a78e9848a6c
Branch commit hash: f4b1919427bf1cc2add57500284f3f4facdb6f77

Query Group	Query Name	Mean Time - Commit (ms)	Mean Time - Master (ms)	Diff
ldbc_snb_is	q32	3.15	5.45	-2.29 (-42.11%)
ldbc_snb_is	q33	13.33	18.64	-5.31 (-28.47%)
recursive_join	recursive-join-sparse	6.56	10.84	-4.28 (-39.47%)

Other queries

Query Group	Query Name	Mean Time - Commit (ms)	Mean Time - Master (ms)	Diff
aggregation	q24	709.02	698.81	10.21 (1.46%)
aggregation	q28	7605.20	7941.83	-336.63 (-4.24%)
filter	q14	59.86	58.77	1.09 (1.86%)
filter	q15	60.63	58.20	2.43 (4.17%)
filter	q16	276.63	274.04	2.59 (0.95%)
filter	q17	380.85	381.02	-0.17 (-0.04%)
filter	q18	1831.54	1823.42	8.13 (0.45%)
filter	zonemap-node	22.86	22.04	0.82 (3.73%)
filter	zonemap-node-lhs-cast	23.13	22.46	0.67 (2.98%)
filter	zonemap-node-null	22.85	22.03	0.82 (3.72%)
filter	zonemap-rel	5604.02	5488.02	116.01 (2.11%)
fixed_size_expr_evaluator	q07	620.65	625.97	-5.32 (-0.85%)
fixed_size_expr_evaluator	q08	903.31	912.32	-9.01 (-0.99%)
fixed_size_expr_evaluator	q09	902.71	910.55	-7.84 (-0.86%)
fixed_size_expr_evaluator	q10	190.71	198.23	-7.52 (-3.79%)
fixed_size_expr_evaluator	q11	189.76	198.80	-9.04 (-4.55%)
fixed_size_expr_evaluator	q12	168.42	175.48	-7.06 (-4.03%)
fixed_size_expr_evaluator	q13	1503.97	1505.00	-1.03 (-0.07%)
fixed_size_seq_scan	q23	45.23	56.25	-11.02 (-19.59%)
join	q29	746.49	851.43	-104.93 (-12.32%)
join	q30	1751.80	1842.69	-90.88 (-4.93%)
join	q31	7.88	7.52	0.36 (4.75%)
join	SelectiveTwoHopJoin	65.31	59.03	6.28 (10.63%)
ldbc_snb_ic	q35	10.44	10.02	0.42 (4.20%)
ldbc_snb_ic	q36	93.95	97.88	-3.93 (-4.02%)
ldbc_snb_is	q34	1.22	1.17	0.06 (4.74%)
limit	push-down-limit-into-distinct	1919.11	2033.71	-114.60 (-5.63%)
multi-rel	multi-rel-large-scan	1446.23	1494.41	-48.19 (-3.22%)
multi-rel	multi-rel-lookup	9.29	9.26	0.03 (0.27%)
multi-rel	multi-rel-small-scan	200.44	172.19	28.25 (16.40%)
order_by	q25	62.07	62.61	-0.54 (-0.86%)
order_by	q26	392.08	380.26	11.82 (3.11%)
order_by	q27	1308.84	1311.51	-2.67 (-0.20%)
recursive_join	recursive-join-bidirection	386.24	372.98	13.26 (3.56%)
recursive_join	recursive-join-dense	7059.80	7140.45	-80.65 (-1.13%)
recursive_join	recursive-join-path	23646.21	23856.18	-209.96 (-0.88%)
recursive_join	recursive-join-trail	7014.65	7108.18	-93.53 (-1.32%)
scan_after_filter	q01	103.60	104.28	-0.68 (-0.65%)
scan_after_filter	q02	89.85	89.86	-0.02 (-0.02%)
shortest_path_ldbc100	q37	84.59	78.04	6.54 (8.38%)
shortest_path_ldbc100	q38	297.64	308.47	-10.83 (-3.51%)
shortest_path_ldbc100	q39	89.08	92.43	-3.35 (-3.62%)
shortest_path_ldbc100	q40	529.34	485.60	43.74 (9.01%)
var_size_expr_evaluator	q03	2140.01	2139.12	0.89 (0.04%)
var_size_expr_evaluator	q04	2142.85	2166.50	-23.65 (-1.09%)
var_size_expr_evaluator	q05	2604.43	2559.38	45.04 (1.76%)
var_size_expr_evaluator	q06	1270.17	1265.16	5.02 (0.40%)
var_size_seq_scan	q19	1363.04	1380.99	-17.94 (-1.30%)
var_size_seq_scan	q20	2648.26	2629.88	18.39 (0.70%)
var_size_seq_scan	q21	2185.00	2220.53	-35.53 (-1.60%)
var_size_seq_scan	q22	109.62	108.58	1.04 (0.96%)

[acquamarin]

I am a bit confused there?
When will the children by empty? Since you always push a value to the createDefaultValue function:

ase LogicalTypeID::UNION: {
        // We can't create a default value for the union since the
        // selected variant is runtime information. Default value
        // is initialized when copying (see Value::copyFromUnion).
        return Value(dataType.copy(), std::vector<std::unique_ptr<Value>>{});