Lazily load project submodules

[Beforerr]

pyspedas.mission and pyspedas.project.mission still work but now lazily loaded
import pyspedas.mission is not supported however.

This pull has breaking changes so we maybe merge it for v2.0

#1050

[Beforerr]

Similar things could be done for analysis modules if desired

[Beforerr]

Benchmark shows that first loading speed improve about 0.5s and average 0.15s

❯ hyperfine "python -c 'import pyspedas'"

Benchmark 1: python -c 'import pyspedas'
  Time (mean ± σ):      1.541 s ±  0.236 s    [User: 2.535 s, System: 0.287 s]
  Range (min … max):    1.421 s …  2.205 s    10 runs
 
  Warning: The first benchmarking run for this command was significantly slower than the rest (2.205 s). This could be caused by (filesystem) caches that were not filled until after the first run. You should consider using the '--warmup' option to fill those caches before the actual benchmark. Alternatively, use the '--prepare' option to clear the caches before each timing run.

Benchmark 1: python -c 'import pyspedas'
  Time (mean ± σ):      1.401 s ±  0.152 s    [User: 2.520 s, System: 0.266 s]
  Range (min … max):    1.301 s …  1.788 s    10 runs
 
  Warning: The first benchmarking run for this command was significantly slower than the rest (1.788 s). This could be caused by (filesystem) caches that were not filled until after the first run. You should consider using the '--warmup' option to fill those caches before the actual benchmark. Alternatively, use the '--prepare' option to clear the caches before each timing run.
 

[Beforerr]

Now the mainly loading cost comes from pytplot and mms compareed to previous #1050 (comment)