comm: complete migration to JSON.jl v1 #1550

Job	Run time
Julia 1 - ubuntu-latest - x64	13m 40s
Julia 1.12 - ubuntu-latest - x64	13m 18s
Julia 1 - macos-latest - x64	19m 26s
Test with `JULIA_NUM_THREADS = 4,2`	13m 1s
Test with `JETLS_DEBUG_LOWERING = true`	12m 44s
Test with `JETLS_DEV_MODE = true`	16m 34s
Test jetls executable	6m 33s
Test LSP.jl	42s
Julia nightly - ubuntu-latest - x64	3m 53s
	1h 39m 51s

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