Prepare Pgvector.EntityFrameworkCore 10.0.0 for EF Core 10 - #63

@ankane as discussed in #59 (comment), this creates a new version of Pgvector.EntityFrameworkCore which targets net10.0 (and EF10) instead of the previous net9.0 (and EF9). The reason for doing this is that net9.0/EF9 are about to go out of support, and targeting net9.0 will start emitting warnings.

I'm proposing to bump the version of Pgvector.EntityFrameworkCore from 0.3.0 to 10.0.0, to align the library's versioning it with the EF's version (as most providers/extensions do) - but if you prefer something else (e.g. 0.4.0) let me know and I'll do that instead.

I will also submit a 2nd PR stacked upon this which bumps yet again, and targets net11.0 and (the upcoming) EF11. This is specifically required for #59, which stops loading vector columns by default (quite important for perf).

Let me know what you think and if you have any concerns, am happy to change things as needed.

Summary

• Set Pgvector.EntityFrameworkCore to version 10.0.0, target only net10.0, and reference stable Npgsql.EntityFrameworkCore.PostgreSQL 10.0.3.
• Move the unchanged design-time build target to build/net10.0 and update compatibility documentation and the changelog.
• Leave the Pgvector and Pgvector.Dapper package versions, targets, and dependency policies unchanged.

This is the bottom layer of a planned two-PR chain. The EF 11 release and IsAutoLoaded convention belong to the follow-up PR; this PR does not complete #59. The package version numbering follows the proposed release plan and is not a claim of maintainer approval.

Validation

• Existing C# suite: 29 passed against local PostgreSQL with pgvector 0.8.2.
• Release package build succeeded; verified lib/net10.0, build/net10.0, package version 10.0.0, and the 10.0.3 provider dependency.
• A separate net10.0 project consumed the packed package successfully and generated the expected design-time services attribute.