use list comprehension in more ToJson impls

[bobzhang]

Summary

• Simplify ToJson implementations across hashset, list, set, deque, priority_queue, immut/priority_queue, and immut/sorted_set to use list comprehension syntax
• Update immut/vector test to use list comprehension
• Follow-up to use list comprehension in ToJson impls #3450

Test plan

• CI passes

🤖 Generated with Claude Code

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[coveralls]

Coverage Report for CI Build 3886

Coverage decreased (-0.002%) to 94.907%

Details

• Coverage decreased (-0.002%) from the base build.
• Patch coverage: 10 of 10 lines across 9 files are fully covered (100%).
• 3 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

3 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
immut/vector/vector.mbt	3	92.48%

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Coverage Stats

Relevant Lines:	15510
Covered Lines:	14720
Line Coverage:	94.91%
Coverage Strength:	220531.03 hits per line

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💛 - Coveralls