chore(examples): add nycflights13 dataset to examples

[gforsyth]

Resolves #8718

As an example:

[ins] In [1]: from ibis.interactive import *

[ins] In [2]: ibis.examples.nycflights13_airports.fetch()
Out[2]: 
┏━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━┳━━━━━━━━━━━━━┳━━━━━━━┳━━━━━━━┳━━━┓
┃ faa    ┃ name                       ┃ lat       ┃ lon         ┃ alt   ┃ tz    ┃ … ┃
┡━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━╇━━━━━━━━━━━━━╇━━━━━━━╇━━━━━━━╇━━━┩
│ string │ string                     │ float64   │ float64     │ int64 │ int64 │ … │
├────────┼────────────────────────────┼───────────┼─────────────┼───────┼───────┼───┤
│ 04G    │ Lansdowne Airport          │ 41.130472 │  -80.619583 │  1044 │    -5 │ … │
│ 06A    │ Moton Field Municipal Air… │ 32.460572 │  -85.680028 │   264 │    -6 │ … │
│ 06C    │ Schaumburg Regional        │ 41.989341 │  -88.101243 │   801 │    -6 │ … │
│ 06N    │ Randall Airport            │ 41.431912 │  -74.391561 │   523 │    -5 │ … │
│ 09J    │ Jekyll Island Airport      │ 31.074472 │  -81.427778 │    11 │    -5 │ … │
│ 0A9    │ Elizabethton Municipal Ai… │ 36.371222 │  -82.173417 │  1593 │    -5 │ … │
│ 0G6    │ Williams County Airport    │ 41.467306 │  -84.506778 │   730 │    -5 │ … │
│ 0G7    │ Finger Lakes Regional Air… │ 42.883565 │  -76.781232 │   492 │    -5 │ … │
│ 0P2    │ Shoestring Aviation Airfi… │ 39.794824 │  -76.647191 │  1000 │    -5 │ … │
│ 0S9    │ Jefferson County Intl      │ 48.053809 │ -122.810644 │   108 │    -8 │ … │
│ …      │ …                          │         … │           … │     … │     … │ … │
└────────┴────────────────────────────┴───────────┴─────────────┴───────┴───────┴───┘

To do this I've added an entry to gen_registry.py that pulls the flight data and converts it to zstd-compressed parquet.

I've also added a pixi.toml and pixi.lock and a short README for the examples folder so other maintainers can start with a little more context.

I should also note that this is very far from perfect -- currently, when running gen_registry.py, the nycflights data DOES get added, but it also removes several entries from the metadata.json file. I've manually removed all of those changes.

The short version, though, is that what gen_registry currently does only provides a subset of our current examples offering.

Description of changes

Issues closed

[gforsyth]

Also, the lock file is enormous and if we'd rather it didn't get checked in, I'm happy to remove it and to pin down the dependencies in the pixi.toml file a little more closely.