fix(core): isolate nested transient instances in static context

[veeceey]

Description

Fixes #16257

When multiple DEFAULT-scoped providers inject the same TRANSIENT -> TRANSIENT chain, the deeply nested transient instances are incorrectly shared. For example:

@Injectable()
class ServiceA {
  constructor(public readonly logger: TransientLogger) {}
}

@Injectable()
class ServiceB {
  constructor(public readonly logger: TransientLogger) {}
}

@Injectable({ scope: Scope.TRANSIENT })
class TransientLogger {
  constructor(public readonly nested: NestedTransient) {}
}

@Injectable({ scope: Scope.TRANSIENT })
class NestedTransient {}

In this scenario, serviceA.logger.nested and serviceB.logger.nested point to the same NestedTransient instance, even though both TransientLogger instances are correctly different.

Root cause

The transient map uses the inquirer's wrapper ID as the key. In STATIC context, getEffectiveInquirer() has a contextId !== STATIC_CONTEXT guard that prevents it from returning the parent inquirer for nested TRANSIENT chains. This means the intermediate TransientLogger wrapper's ID is used as the key regardless of which DEFAULT parent (ServiceA vs ServiceB) initiated the chain — so the nested instance gets shared.

Fix

Introduces getEffectiveInquirerId() which returns a composite key (parentInquirer.id:inquirer.id) for nested TRANSIENT chains in STATIC context. This ensures each resolution path through a different DEFAULT parent produces its own isolated nested instance, without affecting the existing behavior for non-nested cases or REQUEST-scoped contexts.

Also updates TestingInjector.resolveComponentHost() to forward the new inquirerIdOverride parameter.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have read the CONTRIBUTING document
• My commit message follows the conventional commits format
• New unit tests added for nested transient isolation scenarios
• New integration tests added for DEFAULT -> TRANSIENT -> TRANSIENT chains
• All existing tests pass (1990 unit tests, all transient scope integration tests)

[coveralls]

Pull Request Test Coverage Report for Build 4594ff5f-f403-4927-91ad-e3405f57f30c

Details

• 10 of 10 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on fix/issue-16257-transient-isolation-static-context at 89.836%

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Totals
Change from base Build 35a249bb-b90d-4d09-aaec-feede0cafbd4:	89.8%
Covered Lines:	7469
Relevant Lines:	8314

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💛 - Coveralls

[veeceey]

friendly ping - any chance someone could take a look at this? the transient scope isolation issue is kind of subtle but it bites people