Improvements to Value iterators

[jpschorr]

• Implement size_hint for applicable iterators
• rename coerce_to_* methods to coerce_into_* when they take ownership
• reify some iterators rather than use impl Iterator

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

Conformance comparison report

	Base (d93dfe7)	2048c95	+/-
% Passing	89.06%	89.06%	0.00%
✅ Passing	5649	5649	0
❌ Failing	694	694	0
🔶 Ignored	0	0	0
Total Tests	6343	6343	0

Number passing in both: 5649

Number failing in both: 694

Number passing in Base (d93dfe7) but now fail: 0

Number failing in Base (d93dfe7) but now pass: 0

[codecov]

Codecov Report

Patch coverage: 57.62% and project coverage change: -0.21% ⚠️

Comparison is base (191b10e) 81.70% compared to head (39e856e) 81.49%.
Report is 3 commits behind head on main.

❗ Current head 39e856e differs from pull request most recent head e70df4b. Consider uploading reports for the commit e70df4b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #422      +/-   ##
==========================================
- Coverage   81.70%   81.49%   -0.21%     
==========================================
  Files          62       62              
  Lines       15235    15332      +97     
  Branches    15235    15332      +97     
==========================================
+ Hits        12447    12495      +48     
- Misses       2285     2334      +49     
  Partials      503      503              

Files Changed	Coverage Δ
partiql-eval/src/eval/expr/coll.rs	93.49% <0.00%> (-3.97%)	⬇️
partiql-value/src/bag.rs	66.66% <50.00%> (-1.20%)	⬇️
partiql-value/src/lib.rs	93.84% <50.00%> (-2.03%)	⬇️
partiql-value/src/list.rs	53.93% <50.00%> (-0.29%)	⬇️
partiql-value/src/tuple.rs	87.14% <77.27%> (-2.21%)	⬇️
extension/partiql-extension-ion/src/decode.rs	77.63% <100.00%> (+0.21%)	⬆️
partiql-eval/src/eval/evaluable.rs	89.40% <100.00%> (ø)
partiql-eval/src/lib.rs	98.69% <100.00%> (ø)

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[alancai98]

Should we keep this TODO about not hard-coding 'fresh' keys?