load_book: support for fixed tones, smurfgaps flags, no_headers

[mhasself]

• When "special_channel=True" is passed to get_obs, the "untracked" channels are loaded and populate a .tones sub-AxisMan.
• The smurfgaps flags are loaded from the per-stream frame data and put into .flags.smurfgaps_{stream_id}.
• When user passes "no_headers=True", the smurf header fields will not be unpacked (so there is no .primary).

[mhasself]

Addresses #1160. Here's what smurfgaps looks like (obs_id='obs_1745071718_satp1_1111111')

>>> tod.flags
FlagManager(smurfgaps_ufm_mv18[samps], 
 smurfgaps_ufm_mv19[samps], 
 smurfgaps_ufm_mv22[samps], 
 smurfgaps_ufm_mv48r1[samps], 
 smurfgaps_ufm_mv50r2[samps], 
 smurfgaps_ufm_mv51[samps],
 smurfgaps_ufm_mv52r1[samps],
 dets:LabelAxis(11935), samps:OffsetAxis(475151))

>>> for k, v in tod.flags._fields.items():
...   print(k, v.ranges())
... 
smurfgaps_ufm_mv18 [[90134 90171]
 [90172 90322]]
smurfgaps_ufm_mv19 [[90134 90141]]
smurfgaps_ufm_mv22 []
smurfgaps_ufm_mv48r1 []
smurfgaps_ufm_mv50r2 []
smurfgaps_ufm_mv51 [[90134 90138]]
smurfgaps_ufm_mv52r1 [[90134 90220]]

[mhasself]

Also addresses #1190. E.g:

obs_id = 'obs_1744840989_satp1_0000010'
tod = ctx.get_obs(obs_id, special_channels=True)

Then:

>>> tod.tones
AxisManager(stream_id[tdets], band[tdets], channel[tdets], signal[tdets,samps], 
tdets:LabelAxis(23), samps:OffsetAxis(1318))

>>> tod.tones.tdets.vals
array(['ufm_mv52r1_0_38', 'ufm_mv52r1_0_377', 'ufm_mv52r1_2_326',
      ...
      'ufm_mv52r1_6_198', 'ufm_mv52r1_6_362'], dtype='<U16')

>>> tod.tones.signal
array([[ 1.6924602,  1.6927478,  1.6926519, ...,  1.692556 ,  1.6924602,
         1.691885 ],
       [ 2.4248402,  2.4247444,  2.4246483, ...,  2.4244566,  2.4244566,
         2.4244566],
       ...,
       [ 1.2802029,  1.280107 ,  1.280011 , ...,  1.2802987,  1.280107 ,
         1.280011 ]], dtype=float32)

[kmharrington]

Looks good to me!

Any chance there's a way to make operations books automatically load headers but not obs books? I suspect we'll usually want it when operation books are being loaded.

[mhasself]

Any chance there's a way to make operations books automatically load headers but not obs books? I suspect we'll usually want it when operation books are being loaded.

Yes... this seems to be quite a big savings, so it's in place now. At least when you use context.get_obs.

I had assumed that loading headers was cheap, if one were already loading signal. But looks like that's not the case ... my random test suggests 40% increase in load time, when reading headers.

I cleaned up a couple other things. Will merge when tests pass unless there are further concerns.