feat: added bounded options for least squares solvers

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 58.00000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 72.52%. Comparing base (bd3d702) to head (9b1e880). Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
pyTMD/io/model.py	4.76%	19 Missing and 1 partial :warning:
pyTMD/solve/constants.py	75.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #341 +/- ## ========================================== + Coverage 71.65% 72.52% +0.87% ========================================== Files 39 39 Lines 11042 10338 -704 Branches 1522 1384 -138 ========================================== - Hits 7912 7498 -414 + Misses 2632 2375 -257 + Partials 498 465 -33 ``` | [Flag](https://app.codecov.io/gh/tsutterley/pyTMD/pull/341/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tyler+Sutterley) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/tsutterley/pyTMD/pull/341/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tyler+Sutterley) | `72.52% <58.00%> (+0.87%)` | :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=Tyler+Sutterley#carryforward-flags-in-the-pull-request-comment) to find out more.

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