Fix problems in applying `compute_Sv` on combined `EchoData` object

[leewujung]

This PR fixes various problems discovered in applying compute_Sv on combined EchoData object:

• redundancy in computing sound speed when calculating echo range
• forward-fill to take care of the case when ping_time extends beyond the end of time1 for the environmental params
• add bottleneck as dependency as it is needed for xr.DataArray.ffill

TODO:

• [x] add test for cases needing forward fill

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.51%. Comparing base (9f56124) to head (985a3b1). Report is 118 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1328 +/- ## ========================================== + Coverage 83.52% 89.51% +5.98% ========================================== Files 64 11 -53 Lines 5686 1001 -4685 ========================================== - Hits 4749 896 -3853 + Misses 937 105 -832 ``` | [Flag](https://app.codecov.io/gh/OSOceanAcoustics/echopype/pull/1328/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OSOceanAcoustics) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/OSOceanAcoustics/echopype/pull/1328/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OSOceanAcoustics) | `89.51% <100.00%> (+5.98%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OSOceanAcoustics#carryforward-flags-in-the-pull-request-comment) to find out more.

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[ctuguinay]

@leewujung This should be ready for review. I added a test and dropped time1 after the interpolation and ffill.