everyvoice synthesize default file name ( ckpt or step?)

Had a question on on slack, copying it here to keep track / assign to @SamuelLarkin from the thread ( Thank you)

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I have a question about how we are doing checkpointing `ckpt_epochs: 1 ` in EV.
For example, I have a test where I set `max_epochs: 100 ` and training is done.
Logs look like this below .
```
(EveryVoice) [U20-GPSC7]:$ ll logs_and_checkpoints/FeaturePredictionExperiment/base/checkpoints/
total 1.5G
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 'epoch=87-step=1144.ckpt'
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 'epoch=93-step=1222.ckpt'
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 'epoch=96-step=1261.ckpt'
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 'epoch=97-step=1274.ckpt'
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 'epoch=99-step=1300.ckpt'
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 'epoch=99-step=1300-v1.ckpt'
-rw-r----- 1 tes001 nrc_ict 209M Apr 29 16:18 last.ckpt
```
I generated an audio file using that last.ckpt and this was the filename created below after synth..:

`synthesis_output/wav/made-certain-recomme-9229d5cf--default--eng--ckpt\=1300--v_ckpt\=5000000--pred.wav`

Question, is it a bug in everyvoice synthesize where that file name should have been something like this instead:
`made-certain-recomme-9229d5cf--default--eng--ckpt\=100--v_ckpt\=2500000--pred.wav`

Where `ckpt` should be --> 100 ( or 99 depending on how you count...)
and `v_ckpt` should be --> 2.5M since I used our Universal Vocoder ( where I thought we took it a the 2.5M checkpoint...)
OR should "`ckpt=`" be changed for "`step=`" instead when creating the file name on synth to be more precise?

Sam also had this comment : _so I feel it is more that we don't have the proper definition of epoch, ckpt and step_

Where I agree, and I am also wondering about those numbers when using multi-gpu / nodes while training.

Sam was also wondering how many GPUs were used while training our Vocoder / are we doing gradient accumulation?. ( cause we are seeing 2.5M and 5M in the model / not sure what it the right one to use?...)

Start with the EveryVoice synthesize entry point and the checkpoint naming logic that produces the shown output filename. Compare its epoch, step, vocoder checkpoint, multi-GPU, and gradient-accumulation values with the training logs and checkpoint files. Done means the naming behavior and checkpoint terminology are resolved and covered by appropriate validation or documentation.

Written by the indexing model from the issue text.