Improve tx manager hash packing

[mattsse]

trafficstars

Describe the feature

this is currently enforced by a duration budget

https://github.com/paradigmxyz/reth/blob/7a599dc13018acc7f7d206581bf4cd4eb6368091/crates/net/network/src/transactions/mod.rs#L1629-L1640

and always allocates some capacity

https://github.com/paradigmxyz/reth/blob/7a599dc13018acc7f7d206581bf4cd4eb6368091/crates/net/network/src/transactions/fetcher.rs#L422-L429

all of this is a bit hard to read, and a bit suboptimal in general

https://github.com/paradigmxyz/reth/blob/7a599dc13018acc7f7d206581bf4cd4eb6368091/crates/net/network/src/transactions/fetcher.rs#L78-L84

TODO

• create a more efficient implementation of txhash fetching
• all the packing logic should be testable in isolation

@0xKarl98

Additional context

No response