Merge bitcoin/bitcoin#28077: I2P: also sleep after errors in Accept() & destroy the session if we get an unexpected error

5c8e15c451ec870b9dd4eb843ec6ca3ba64cda4f i2p: destroy the session if we get an unexpected error from the I2P router (Vasil Dimov)
762404a68c114e8831cdfae937627174544b55a7 i2p: also sleep after errors in Accept() (Vasil Dimov)

Pull request description:

  ### Background

  In the `i2p::sam::Session` class:

  `Listen()` does:
  * if the session is not created yet
    * create the control socket and on it:
    * `HELLO`
    * `SESSION CREATE ID=sessid`
    * leave the control socked opened
  * create a new socket and on it:
  * `HELLO`
  * `STREAM ACCEPT ID=sessid`
  * read reply (`STREAM STATUS`), `Listen()` only succeeds if it contains `RESULT=OK`

  Then a wait starts, for a peer to connect. When connected,

  `Accept()` does:
  * on the socket from `STREAM ACCEPT` from `Listen()`: read the Base64 identification of the connecting peer

  ### Problem

  The I2P router may be in such a state that this happens in a quick succession (many times per second, see https://github.com/bitcoin/bitcoin/issues/22759#issuecomment-1609907115): `Listen()`-succeeds, `Accept()`-fails.

  `Accept()` fails because the I2P router sends something that is not Base64 on the socket: `STREAM STATUS RESULT=I2P_ERROR MESSAGE="Session was closed"`

  We only sleep after failed `Listen()` because the assumption was that if `Accept()` fails then the next `Listen()` will also fail.

  ### Solution

  Avoid filling the log with "Error accepting:" messages and sleep also after a failed `Accept()`.

  ### Extra changes

  * Reset the error waiting time after one successful connection. Otherwise the timer will remain high due to problems that have been solved long time in the past.

  * Increment the wait time less aggressively.

  * Handle the unexpected "Session was closed" message more gracefully (don't log stupid messages like `Cannot decode Base64: "STREAM STATUS...`) and destroy the session right way.

ACKs for top commit:
  achow101:
    ACK 5c8e15c451ec870b9dd4eb843ec6ca3ba64cda4f
  jonatack:
    re-ACK 5c8e15c451ec870b9dd4eb843ec6ca3ba64cda4f

Tree-SHA512: 1d47958c50eeae9eefcb668b8539fd092adead93328e4bf3355267819304b99ab41cbe1b5dbedbc3452c2bc389dc8330c0e27eb5ccb880e33dc46930a1592885

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