FXC-1530: add total current normalization to UniformCurrentSource

[dmarek-flex]

Note

Medium Risk
Touches a core source model and adds new validation-time warnings plus a new normalization mode; while defaults are preserved, behavior and user-visible logs change and could affect downstream workflows relying on implicit defaults.

Overview
Adds a new UniformCurrentSource.current_amplitude_definition field ("density" default, or "total") to support size-independent total-current injection, and updates the UniformCurrentSource docs/example accordingly.

Introduces a post-init validation warning when current_amplitude_definition is not explicitly set, signaling a future default change from "density" to "total", and propagates the new field into JSON schemas and key call sites (e.g., rectangular lumped port source creation) plus broad test updates/new warning coverage.

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[github-actions]

Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/source/current.py (100%)

Summary

• Total: 8 lines
• Missing: 0 lines
• Coverage: 100%

[weiliangjin2021]

Just a small comment on naming.

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[dmarek-flex]

I added a validation warning about changing the default behavior in the future. Is this how we typically do this?

[momchil-flex]

Yeah, generally we've also been trying to say in which version exactly we would change the behavior. But if you're not sure (e.g. if we might end up changing it in rf but not in photonics) could leave as is.

So you preemptively updated tests to the new behavior?

[dmarek-flex]

So you preemptively updated tests to the new behavior?

I had to change a lot of tests since they were emitting the warning, and then the AssertLogLevel would fail the test. Other tests, I changed just to remove the warning and preempt the new default behavior.