feat: add path refresher strategy

[jpcsmith]

Add a path strategy that periodically refreshes paths.

Remaining tasks:

• add an integration test that combines the async path strategy and path refresher.

[jpcsmith]

@mlegner Could you have a look at this when you have a moment please? It's mostly done with the exception of needed to add an integration test.

[github-actions]

Package	Line Rate	Health
crates/scion/src	80%	✔
crates/scion-proto/src/packet	81%	✔
crates/scion-proto/src/scmp	77%	✔
crates/scion/src/daemon	91%	✔
crates/scion/src/pan/path_strategy	83%	✔
crates/scion-proto/src/address	70%	➖
crates/scion-proto/src/packet/headers	85%	✔
crates/scion-proto/src/path	83%	✔
crates/scion-proto/src/path/standard	92%	✔
crates/scion-proto/src/reliable	95%	✔
crates/scion-proto/src	80%	✔
crates/scion-proto/src/path/metadata	100%	✔
crates/scion/src/pan	76%	✔
Summary	80% (1809 / 2267)	✔

[mlegner]

Thanks for the PR, @jpcsmith, I will take a look today.

[mlegner]

Thanks for implementing this, @jpcsmith.

Everything looks good from my side. I will take a look at the tests together with the missing integration test.

[mlegner]

Wow, I think this test suite sets a new standard for future code. 🤩

All looks good, just a few nits and minor remarks.