Fix RULE-0-2-4/A0-1-3 false positives for private functions

[castler]

Description

Three categories of false positive are addressed:

1. **Static call targets not recognised** — the original check used
   only `getTarget(call)` from DynamicCallGraph, which resolves
   virtual dispatch.  For private (non-virtual) member functions and
   private static functions that are called directly, CodeQL sometimes
   cannot resolve a dynamic target and the function was incorrectly
   reported as unused.  The new `functionIsCalled(fn)` predicate
   combines the dynamic-graph result with a direct
   `FunctionCall.getTarget()` lookup so that statically-dispatched
   calls are always counted as a use.

2. **Template instantiations called only via direct dispatch** — the
   template-instantiation guard that suppresses a report when "some
   instantiation is called" was also using only `getTarget(_)`.
   Switching it to `functionIsCalled(_)` makes it consistent.

3. **Pure virtual private member functions** — RULE-0-2-4 and A0-1-3
   require that private member functions be *used*.  A pure virtual
   function (`= 0`) is an interface contract that must be overridden
   by derived classes; it has no body of its own and cannot be
   "called" directly.  Excluding `PureVirtualFunction` from the
   `LocalFunction` class prevents spurious reports on these.

Fixes #1168

Change request type

• Release or process automation (GitHub workflows, internal scripts)
• Internal documentation
• External documentation
• Query files (.ql, .qll, .qls or unit tests)
• External scripts (analysis report or other code shipped as part of a release)

Rules with added or modified queries

• No rules added
• Queries have been added for the following rules:
  • rule number here
• Queries have been modified for the following rules:
  • RULE-0-2-4
  • A0-1-3

Release change checklist

A change note (development_handbook.md#change-notes) is required for any pull request which modifies:

• The structure or layout of the release artifacts.
• The evaluation performance (memory, execution time) of an existing query.
• The results of an existing query in any circumstance.

If you are only adding new rule queries, a change note is not required.

Author: Is a change note required?

• Yes
• No

🚨🚨🚨
Reviewer: Confirm that format of shared queries (not the .qll file, the
.ql file that imports it) is valid by running them within VS Code.

• Confirmed

Reviewer: Confirm that either a change note is not required or the change note is required and has been added.

• Confirmed

Query development review checklist

For PRs that add new queries or modify existing queries, the following checklist should be completed by both the author and reviewer:

Author

• Have all the relevant rule package description files been checked in?
• Have you verified that the metadata properties of each new query is set appropriately?
• Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
• Are the alert messages properly formatted and consistent with the style guide?
• Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
• Does the query have an appropriate level of in-query comments/documentation?
• Have you considered/identified possible edge cases?
• Does the query not reinvent features in the standard library?
• Can the query be simplified further (not golfed!)

Reviewer

• Have all the relevant rule package description files been checked in?
• Have you verified that the metadata properties of each new query is set appropriately?
• Do all the unit tests contain both "COMPLIANT" and "NON_COMPLIANT" cases?
• Are the alert messages properly formatted and consistent with the style guide?
• Have you run the queries on OpenPilot and verified that the performance and results are acceptable?
  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
• Does the query have an appropriate level of in-query comments/documentation?
• Have you considered/identified possible edge cases?
• Does the query not reinvent features in the standard library?
• Can the query be simplified further (not golfed!)