Add exp2 numpy op

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.68293% with 9 lines in your changes missing coverage. Please review.

Project coverage is 82.12%. Comparing base (1354fde) to head (f640f25).

Files with missing lines	Patch %	Lines
keras/src/ops/numpy.py	90.56%	4 Missing and 1 partial :warning:
keras/src/backend/tensorflow/numpy.py	85.71%	3 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #20504 +/- ## ========================================== + Coverage 82.10% 82.12% +0.01% ========================================== Files 515 515 Lines 47670 47711 +41 Branches 7468 7474 +6 ========================================== + Hits 39141 39182 +41 Misses 6721 6721 Partials 1808 1808 ``` | [Flag](https://app.codecov.io/gh/keras-team/keras/pull/20504/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | Coverage Δ | | |---|---|---| | [keras](https://app.codecov.io/gh/keras-team/keras/pull/20504/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `81.97% <92.68%> (+0.01%)` | :arrow_up: | | [keras-jax](https://app.codecov.io/gh/keras-team/keras/pull/20504/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `65.04% <54.47%> (-0.01%)` | :arrow_down: | | [keras-numpy](https://app.codecov.io/gh/keras-team/keras/pull/20504/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `60.01% <58.53%> (+<0.01%)` | :arrow_up: | | [keras-tensorflow](https://app.codecov.io/gh/keras-team/keras/pull/20504/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `66.03% <64.22%> (-0.01%)` | :arrow_down: | | [keras-torch](https://app.codecov.io/gh/keras-team/keras/pull/20504/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=keras-team) | `64.96% <59.34%> (-0.01%)` | :arrow_down: | 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=keras-team#carryforward-flags-in-the-pull-request-comment) to find out more.

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