add oceans and parallelism functionality

[amir16yp]

This PR does two things:

1. Make a lot of the logic implement parallelism to better utilize multiple CPU cores
2. Add an option for generating oceans (in elevation-enabled maps only) by providing a shapefile containing polygons of global water bodies. You can download this data from https://osmdata.openstreetmap.de/download/water-polygons-split-4326.zip

Overall the only thing that is left to do here is benchmark the previous release vs this PR (without oceans), and perhaps later you could implement a way for it to automatically download the shapefile data

[amir16yp]

This might break the GUI progress bar, i just noticed this

[amir16yp]

this makes performance worse apparently

[louis-e]

retrigger-benchmark

[github-actions]

⏱️ Benchmark run finished in 1m 4s
🧠 Peak memory usage: 912 MB

📈 Compared against baseline: 69s
🧮 Delta: -5s
🔢 Commit: 83e9a63

⚠️ This PR worsens generation time.

You can retrigger the benchmark by commenting retrigger-benchmark.

[amir16yp]

⏱️ Benchmark run finished in 1m 6s 🧠 Peak memory usage: 934 MB

📈 Compared against baseline: 69s 🧮 Delta: -3s 🔢 Commit: 83e9a63

🟢 Generation time is unchanged.

You can retrigger the benchmark by commenting retrigger-benchmark.

is this good or bad? @louis-e

[louis-e]

Don't worry about the benchmark bot yet, I just reenabled it. But it's good! If the generation time would exceed a certain threshold, it would mention it in its comment.

[amir16yp]

⏱️ Benchmark run finished in 1m 29s 🧠 Peak memory usage: 935 MB

📈 Compared against baseline: 69s 🧮 Delta: 20s 🔢 Commit: 83e9a63

🚨 This PR drastically worsens generation time.

You can retrigger the benchmark by commenting retrigger-benchmark.

well shit.
it's the parallelization implementation for sure. the ocean generation wasn't enabled in this benchmark

[amir16yp]

i shouldve kept the original implementation of floodfill atp. my problem with it is that when generating oceans is that it would timeout, which causes very little of the actual ocean to be generated (see image)