test: regression test for @container mixin parameter variable resolution

[Copilot]

Using mixin parameters as both the container name and query condition in @container at-rules failed with "variable @bp is undefined" in Less 4.4.2–4.5.1.

@width: 125px;

.mixin(@container-name; @bp) {
  @container @container-name (width < @bp) {
    display: none;
  }
}

.foo {
  .mixin(name, @width);  // Previously: "variable @bp is undefined"
  color: red;
}

The underlying bugs were fixed in v4.6.0 via three separate commits:

• QueryInParens.eval rewrite — old code mutated node state in-place and conditionally restored from a deep copy only when variable declarations were found in frames; rewritten to always return a fresh evaluated node, eliminating the mutation/context-sensitivity
• _evaluated flag on Container — prevents double evaluation when the container node is re-encountered in the parent ruleset's eval loop after being returned from the mixin
• functionRegistry null guard — context.frames[0].functionRegistry.inherit() now guarded against undefined, matching the defensive pattern in mixin-definition.js

This PR adds the missing regression test covering variable container names combined with variable query conditions inside mixin calls, including multiple calls with differing parameters.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Mixins with parameters do not work properly</issue_title>
<issue_description>To reproduce:

Try this code in Playground:

@width: 125px;

.mixin(@container-name; @bp) {
  @container @container-name (width < @bp) {
    display: none;
  }
}

.foo {
  .mixin(name, @width);
  color: red;
}

Current behavior:

Does not compile with an error

variable @bp is undefined

Expected behavior:

Compiles to

.foo {
  color: red;
}
@container name (width < 125px) {
  .foo {
    display: none;
  }
}

Environment information:

• less version: 4.4.2
  </issue_description>

<agent_instructions>Can you make a branch / PR with a fix for this? Probably something in @container parsing and evaluation?</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@matthew-dean I'm not sure the Dosubot is correct -- this is probably a bug specifically in the `@container` at-rule parsing & evaluation (or general at-rule parsing & evaluation).

• Fixes Mixins with parameters do not work properly #4376

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