feat: lossless Timestamp{Nanosecond} DEPEND_TIME coordinate

[Beforerr]

depend_time converted Float64 Unix seconds via unix2datetime, truncating to milliseconds.

• Now yields Timestamp{Nanosecond}, rounding Float64 seconds to the microsecond (their real resolution near the present). Plain Durations.unix2timestamp truncates, which misses the intended ns count for ~75% of ms-valued inputs (e.g. .123 -> .122999808).

• Adds Durations dep

• Swapped DEPEND_TIME coordinate eltype changes from DateTime to Timestamp{Nanosecond}

• Widens compat to CommonDataFormat 0.3 (Fix TT2000 leap-second read; promote DateTime/Timestamp to the CDF epoch types CommonDataFormat.jl#74)

• The SubVariable test endpoints move off record times (a ms DateTime t1 falls before the record at 16:27:35.676234651 under 0.3's ns-exact comparison)

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/variable.jl	66.66%	1 Missing ⚠️

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[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	main	7ca2738...	main / 7ca2738...
clip/dataset-epoch	7.26 ± 0.33 μs	7.16 ± 0.34 μs	1.01 ± 0.067
clip/dataset-variable	3.73 ± 0.12 μs	3.64 ± 0.12 μs	1.03 ± 0.047
clip/variable	8.57 ± 1.9 μs	8.24 ± 2 μs	1.04 ± 0.34
concat/dataset/epoch	1.98 ± 0.1 μs	1.94 ± 0.08 μs	1.02 ± 0.066
concat/dataset/variable	2.1 ± 0.1 μs	2.09 ± 0.071 μs	1.01 ± 0.059
concat/variable/array	1.8 ± 0.35 μs	1.88 ± 0.36 μs	0.96 ± 0.26
concat/variable/construct	3.98 ± 0.2 μs	3.94 ± 0.18 μs	1.01 ± 0.069
dimarray/clip	22.3 ± 1.1 μs	22.3 ± 1.2 μs	0.999 ± 0.07
dimarray/concat	22.9 ± 1.9 μs	22.2 ± 1.6 μs	1.03 ± 0.11
dimarray/single	9.38 ± 0.47 μs	8.84 ± 0.45 μs	1.06 ± 0.076
metadata/dataset	30 ± 0 ns	30 ± 0 ns	1 ± 0
metadata/dim	3.11 ± 0.09 μs	2.91 ± 0.071 μs	1.07 ± 0.041
sanitize/float-3d	12.4 ± 1.9 μs	13 ± 2.2 μs	0.951 ± 0.22
sanitize/int8	1.71 ± 0.05 μs	1.76 ± 0.059 μs	0.972 ± 0.043
sanitize/omni-v	2.25 ± 0.17 μs	2.21 ± 0.19 μs	1.02 ± 0.12
variable/disk/broadcast-realized	5.79 ± 0.84 μs	5.57 ± 1.3 μs	1.04 ± 0.28
variable/disk/maximum	3.27 ± 0.44 μs	3.26 ± 0.41 μs	1 ± 0.19
variable/disk/sum	3.04 ± 8.9 μs	3.1 ± 8.6 μs	0.978 ± 3.9
variable/materialize/elfin-flux	2.56 ± 0.51 μs	2.54 ± 0.57 μs	1.01 ± 0.3
variable/materialize/omni-v	0.461 ± 0.11 μs	0.461 ± 0.1 μs	1 ± 0.32
variable/materialized/broadcast	3.12 ± 0.38 μs	3.04 ± 0.39 μs	1.03 ± 0.18
variable/materialized/maximum	0.591 ± 0.01 μs	0.591 ± 0 μs	1 ± 0.017
variable/materialized/sum	0.34 ± 0.01 μs	0.331 ± 0.001 μs	1.03 ± 0.03
time_to_load	0.203 ± 0.0049 s	0.214 ± 0.0035 s	0.951 ± 0.028

Memory benchmarks

	main	7ca2738...	main / 7ca2738...
clip/dataset-epoch	0.099 k allocs: 6.66 kB	0.099 k allocs: 6.66 kB	1
clip/dataset-variable	0.047 k allocs: 4.06 kB	0.047 k allocs: 4.06 kB	1
clip/variable	0.068 k allocs: 0.0378 MB	0.068 k allocs: 0.0378 MB	1
concat/dataset/epoch	0.037 k allocs: 3.17 kB	0.037 k allocs: 3.17 kB	1
concat/dataset/variable	0.037 k allocs: 3.17 kB	0.037 k allocs: 3.17 kB	1
concat/variable/array	25 allocs: 12.4 kB	25 allocs: 12.4 kB	1
concat/variable/construct	29 allocs: 5.23 kB	29 allocs: 5.23 kB	1
dimarray/clip	0.237 k allocs: 16.4 kB	0.237 k allocs: 16.4 kB	1
dimarray/concat	0.197 k allocs: 0.0447 MB	0.197 k allocs: 0.0447 MB	1
dimarray/single	0.067 k allocs: 15.5 kB	0.067 k allocs: 15.5 kB	1
metadata/dataset	0 allocs: 0 B	0 allocs: 0 B
metadata/dim	0.041 k allocs: 3.3 kB	0.041 k allocs: 3.3 kB	1
sanitize/float-3d	27 allocs: 28.7 kB	27 allocs: 28.7 kB	1
sanitize/int8	22 allocs: 2.94 kB	22 allocs: 2.94 kB	1
sanitize/omni-v	24 allocs: 3.95 kB	24 allocs: 3.95 kB	1
variable/disk/broadcast-realized	24 allocs: 0.0561 MB	24 allocs: 0.0561 MB	1
variable/disk/maximum	12 allocs: 28 kB	12 allocs: 28 kB	1
variable/disk/sum	12 allocs: 28 kB	12 allocs: 28 kB	1
variable/materialize/elfin-flux	12 allocs: 28 kB	12 allocs: 28 kB	1
variable/materialize/omni-v	9 allocs: 3.29 kB	9 allocs: 3.29 kB	1
variable/materialized/broadcast	3 allocs: 27.6 kB	3 allocs: 27.6 kB	1
variable/materialized/maximum	0 allocs: 0 B	0 allocs: 0 B
variable/materialized/sum	0 allocs: 0 B	0 allocs: 0 B
time_to_load	0.2 k allocs: 11.7 kB	0.2 k allocs: 11.7 kB	1