Make the points in cirq_google v2 proto to be double

[BichengYing]

In order to make it forward and backward compatible, i added an extra field points_fl64 and

1. serialization phase: always write to both float points and double points_fl64
2. deserialization phase: use points_fl64 first if it presented, if not, fall back to points.

It will temporary make the communication cost slightly higher since we communicating two points. But it will be make the transition much easier.

UPDATE: added the double field for LinSpace and Const as well.

[pavoljuhas]

Consider marking the old points with [deprecated = true] and adding a comment that the point_list should be used instead.

[BichengYing]

Yes, this is a good practice but we cannot add it [deprecated = true] for now (avoid unnecessary warning) because before we roll-out the latest version into the servers of all machines, this field is still used. I will add a comment first.

[pavoljuhas]

IIUC, deprecated fields are usable just as before except they might show deprecation warnings when used. Such warnings can be helpful to identify client code that uses the old fields.

[BichengYing]

But because of current dual writting mechanism, this warning will be popped out always while the user has no action to do when saw this warning. I feel this will confuse the external users. So I still think this [deprecated = true] should be added after all servers are updated and we stopped the dual write mechanism .

[senecameeks]

I think we also need to extend Linspace and ConstValue to make sure they're consistent.(http://shortn/_TLCXefjbb8)

[BichengYing]

Ok, done. Note ConstValue used oneof, hence, the dual-write trick cannot work here. That one will be switched at last

[BichengYing]

Also, fyi, to make the naming consistently, I use points_fl64, first_point_fl64 and, last_point_fl64.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.68%. Comparing base (07fb131) to head (fb99ea0).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7498   +/-   ##
=======================================
  Coverage   98.68%   98.68%           
=======================================
  Files        1091     1091           
  Lines       96853    96884   +31     
=======================================
+ Hits        95579    95610   +31     
  Misses       1274     1274           

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[pavoljuhas]

LGTM with some small suggestions.

[pavoljuhas]

Nit - consider renaming to points_double here and similarly in Linspace for consistency with ConstValue.double_value.

[BichengYing]

ok

[senecameeks]

LGTM