Bump v0.15.2

[lkdvos]

This PR bumps the version to v0.15.2 (and small fixes in the tutorial docs).

The release notes could be:

Release notes:

TensorKit v0.15.2 contains some changes with respect to how objects are printed. By default, tensors now no longer print their data, and only print their spaces. To inspect the data of a tensor `t`, `blocks(t)` and `subblocks(t)` can be used to print and alter the data in different forms.

We've also updated our compatibility to TensorKitSectors v0.3, which entails some internal consistency naming changes and improvements but should otherwise not affect users. This does provide a step towards full support of multi-fusion categories in TensorKit (Shout-out to @borisdevos for this work).

This patch release also contains fixes and performance improvements:
- The issue with multiple truncation schemes (`TruncationIntersection`) has been solved (#300)
- Some unnecessary allocations in the reverse rules for contractions and tensor products have been avoided (#306)
- The test suite was refactored and split into several groups to reduce the total CI runtime and improve local selective running of the tests (#298)

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[github-actions]

After the build completes, the updated documentation will be available here

[lkdvos]

Unfortunately there are still some instabilities (sensitive to RNG) in the AD tests, but I don't immediately have the time to solve this. Ultimately this doesn't really affect downstream so I'll merge and release here.