Akka.Remote: Endpoint actor cleanup

[Aaronontheweb]

Changes

Removing lots of TBDs and applying some refactoring suggestions

Checklist

For significant changes, please ensure that the following have been completed (delete if not relevant):

• This change follows the Akka.NET API Compatibility Guidelines.
• This change follows the Akka.NET Wire Compatibility Guidelines.
• I have reviewed my own pull request.

Latest dev Benchmarks

All benchmarks are on .NET 8

OSVersion:                         Unix 6.9.3.76060903
ProcessorCount:                    16
ClockSpeed:                        0 MHZ
Actor Count:                       32
Messages sent/received per client: 200000  (2e5)
Is Server GC:                      True
Thread count:                      43

Num clients, Total [msg], Msgs/sec, Total [ms], Start Threads, End Threads
         1,  200000,    107182,    1866.33,            43,              69
         5, 1000000,    373972,    2674.02,            77,              83
        10, 2000000,    781861,    2558.60,            91,              92
        15, 3000000,    713267,    4206.47,           100,             100
        20, 4000000,    617284,    6480.24,           108,             100
        25, 5000000,    650449,    7687.26,           108,              92
        30, 6000000,    654736,    9164.88,           100,              84

This PR's Benchmarks

OSVersion:                         Unix 6.9.3.76060903
ProcessorCount:                    16
ClockSpeed:                        0 MHZ
Actor Count:                       32
Messages sent/received per client: 200000  (2e5)
Is Server GC:                      True
Thread count:                      43

Num clients, Total [msg], Msgs/sec, Total [ms], Start Threads, End Threads
         1,  200000,    112423,    1779.70,            43,              68
         5, 1000000,    322581,    3100.94,            76,              84
        10, 2000000,    666001,    3003.86,            92,              92
        15, 3000000,    730105,    4109.93,           100,             104
        20, 4000000,    755288,    5296.69,           112,             104
        25, 5000000,    786411,    6358.78,           112,              96
        30, 6000000,    698000,    8596.72,           104,              96

[Aaronontheweb]

Detailed my changes - doesn't look like perf was negatively impacted at all (in fact, looks a bit better but honestly that's within / near MoE)

[Aaronontheweb]

Moved all of the local functions to after the return statement

[Aaronontheweb]

Removed recursion in favor of loops

[Aaronontheweb]

Made both this method and WritePrioLoop no longer use recursion

[Arkatufus]

LGTM