*Session attributes handling enhancement and TcpSocketSession cleanup

[skrchnavy]

• Session.attrs table enhanced to support getter and setter methods, not only values
• VI_ATTR_TMO_VALUE attribute handling unified to setup also self.timeout as value holder (can be used in sessions and is set to 'python' timeout - seconds as float or None for infinite)
  • _get_timeout/_set_timeout methods added and updated for places where external lib timeout is setup.
  • GPIBInstrSessiontimeout handling corrected (tested without HW if correct value is calculated in different conditions)
• TCPIP Socket Session supports additional attributes (were not implemented)
  • Session.attrs table used for implementation with getters and setters
  • code cleanup to remove class attributes and use instance attributes
  • _pending_buffer is main buffer for handling received data, removed copying from temp buffer (out) and pending buffer

[skrchnavy]

@MatthieuDartiailh code tested and ready for final review

[MatthieuDartiailh]

I may need some time to review this. Hopefully I will merge sometimes next week.

[MatthieuDartiailh]

One stupid question: shouldn't timeout on the TCPIP session be a private attribute rather than a public one ? From my understanding it should only be set through the visa attribute and not directly.

[skrchnavy]

Further changes / fixes in timeout handling added, some comments applied).

Regarding Session.timeout attribute: it is protected but also 'Session.attrs,Session.interfaceorSession.parsed` are protected. Candidate for writing new issue for this kind of refactoring.

How to cope with the SUCCESS naming convention? spread across Sessions. Which is prefered? (I like StatusCode.success way as it is used for reast of status codes and short enough.)

[skrchnavy]

@MatthieuDartiailh #118 have to be resolved (merged or closed) before this issue (in conflict)

[MatthieuDartiailh]

Merging. Thanks again @skrchnavy

bors r+

[bors[bot]]

Build succeeded

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