Payload length checking, error rework & rust fmt pass

[codecov[bot]]

Codecov Report

Patch coverage: 99.86% and project coverage change: -0.35 :warning:

Comparison is base (2607000) 99.62% compared to head (698e9ef) 99.27%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #47 +/- ## ========================================== - Coverage 99.62% 99.27% -0.35% ========================================== Files 51 114 +63 Lines 21945 29196 +7251 ========================================== + Hits 21863 28985 +7122 - Misses 82 211 +129 ``` | [Impacted Files](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid) | Coverage Δ | | |---|---|---| | [etherparse/src/internet/ip\_number\_impl.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvaW50ZXJuZXQvaXBfbnVtYmVyX2ltcGwucnM=) | `100.00% <ø> (ø)` | | | [etherparse/src/packet\_decoder.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvcGFja2V0X2RlY29kZXIucnM=) | `99.89% <ø> (ø)` | | | [etherparse/src/packet\_filter.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvcGFja2V0X2ZpbHRlci5ycw==) | `100.00% <ø> (ø)` | | | [etherparse/src/packet\_slicing.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvcGFja2V0X3NsaWNpbmcucnM=) | `99.90% <ø> (ø)` | | | [etherparse/src/test\_gens/mod.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvdGVzdF9nZW5zL21vZC5ycw==) | `100.00% <ø> (ø)` | | | [etherparse/src/test\_packet.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvdGVzdF9wYWNrZXQucnM=) | `100.00% <ø> (ø)` | | | [etherparse/src/transport/icmp\_echo\_header.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvdHJhbnNwb3J0L2ljbXBfZWNob19oZWFkZXIucnM=) | `100.00% <ø> (ø)` | | | [...se/src/transport/icmpv4/dest\_unreachable\_header.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvdHJhbnNwb3J0L2ljbXB2NC9kZXN0X3VucmVhY2hhYmxlX2hlYWRlci5ycw==) | `100.00% <ø> (ø)` | | | [etherparse/src/transport/icmpv4/mod.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvdHJhbnNwb3J0L2ljbXB2NC9tb2QucnM=) | `100.00% <ø> (ø)` | | | [...e/src/transport/icmpv4/parameter\_problem\_header.rs](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid#diff-ZXRoZXJwYXJzZS9zcmMvdHJhbnNwb3J0L2ljbXB2NC9wYXJhbWV0ZXJfcHJvYmxlbV9oZWFkZXIucnM=) | `100.00% <ø> (ø)` | | | ... and [104 more](https://codecov.io/gh/JulianSchmid/etherparse/pull/47?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid) | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Julian+Schmid)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.