Chore: rename PVector to PVec

[connortsui20]

Since it will be quite similar to Vec from the standard library.

[codecov]

Codecov Report

❌ Patch coverage is 56.86275% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.42%. Comparing base (2f09c15) to head (8afab09).

Files with missing lines	Patch %	Lines
vortex-vector/src/primitive/vector_mut.rs	57.69%	11 Missing ⚠️
vortex-vector/src/primitive/generic.rs	0.00%	7 Missing ⚠️
vortex-vector/src/primitive/generic_mut.rs	57.14%	3 Missing ⚠️
vortex-vector/src/primitive/vector.rs	75.00%	1 Missing ⚠️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[gatesn]

Everything in this crate is called Vector, I think we should be consistent with that rather than stdlib.