compat for new pandas

[knaaptime]

hey, thanks again for this package. Looks like things are broken with newer versions of pandas, so this grabs the latest commits I could find from the UDST branches, then makes a few updates to get things running again.

I haven't tested thoroughly, but I think this gets things in running order

[d-wasserman]

Thank you for this!

[waddell]

Thank you for assembling this, Eli. UDST has resumed active maintenance of UrbanAccess, and we have completed an initial maintainer review.

This PR is valuable, but it is much broader than a Pandas compatibility patch: relative to dev, it contains 79 commits and changes 30 files, combining previously unmerged UDST work by @sablanchard and @jessicacamacho with the newer compatibility commits. We are treating it as the primary source for the recovery work, with authorship preserved, rather than merging the full branch as-is.

Initial validation on Python 3.12 found:

• installation succeeds with current packaging tools;
• NumPy 2 testing is blocked at collection by the released Pandana 0.7 ABI incompatibility;
• with NumPy 1.26 and compatible SciPy, 132 tests passed before the network-dependent tail was interrupted, with 84 failures and 37 errors remaining;
• representative failures include additional removed Pandas APIs, positional indexing assumptions, changed dtype behavior, and network-dependent tests.

The next step is to establish CI and decompose the accumulated branch work into reviewable compatibility and feature units. We will preserve credit for the incorporated commits and coordinate this with the Pandana compatibility release.

Tracked in #95. @sablanchard is the UDST technical owner for this work.