[BUG][code-analyzer] sfge: calling toString() on an enum aborts the entry point (UnimplementedMethodException)

### Have you tried to resolve this issue yourself first?

- [x] I confirm I have gone through the above steps and still have an issue to report.

### Bug Description

**Engine:** `sfge` (Salesforce Graph Engine) · **Rule:** `ApexFlsViolation` (DevPreview) · **Selector:** `--rule-selector sfge`

`ApexEnumValue.apply` implements only `name()`, `ordinal()` and (when indeterminate) `equals()`, then falls through to `throw new UnimplementedMethodException(this, vertex)` at `ApexEnumValue.java:123`.

`toString()` is universal in Apex — every enum inherits it — so any path that calls it on an enum value aborts.

```apex
Schema.DisplayType dt = Account.Name.getDescribe().getType();
a.Description = dt.toString();
```

### Output / Logs

```shell
UnimplementedMethodException: ApexEnumValue:toString, vertex=MethodCallExpressionVertex{fullMethodName=dt.toString, ...}:
com.salesforce.graph.symbols.apex.ApexEnumValue.apply(ApexEnumValue.java:123);
com.salesforce.graph.symbols.PathScopeVisitor.handleApexValueMethod(PathScopeVisitor.java:1487);
com.salesforce.graph.symbols.PathScopeVisitor.afterVisit(PathScopeVisitor.java:1242); ...
```

### Steps To Reproduce

1. Create an empty SFDX project (`sfdx-project.json` with a single `force-app` package directory).
2. Add `force-app/main/default/classes/EnumToString.cls` with the class shown below, plus a standard `EnumToString.cls-meta.xml` (apiVersion 62.0).
3. Add `code-analyzer.yml`:
```yaml
engines:
sfge:
java_thread_timeout: 900000
java_thread_count: 4
```
4. Run:
```
sf code-analyzer run --rule-selector sfge --workspace . --config-file code-analyzer.yml
```
5. The run reports an `InternalExecutionError` for the entry point instead of analysing it. That entry point yields no `ApexFlsViolation` findings at all, and nothing in the summary indicates coverage was lost.

```apex
public with sharing class EnumToString {
@AuraEnabled
public static void run() {
Schema.DisplayType dt = Account.Name.getDescribe().getType();
Account a = new Account();
a.Description = dt.toString();
insert a;
}
}
```

### Expected Behavior

`toString()` on an enum should resolve like `name()` does — returning the value name when determinate, and an indeterminate string otherwise. Suggested fix: handle `toString` alongside `METHOD_NAME` in `ApexEnumValue.apply`, and add it to `INDETERMINANT_VALUE_PROVIDERS`.

More generally, an unmodelled method on a known value type should degrade to an indeterminate value rather than abort the entry point.

### Operating System

macOS 26.5.2

### Salesforce CLI Version

@salesforce/cli/2.147.7 darwin-arm64 node-v24.5.0

### Code Analyzer Plugin (code-analyzer) Version

code-analyzer 5.15.0

### Node Version

v24.5.0

### Java Version

openjdk version "11.0.32" 2026-07-21

### Python Version

N/A

### Additional Context (Screenshots, Files, etc)

In our codebase this accounts for 8 occurrences across 4 distinct `@AuraEnabled` entry points — the highest count of any single unimplemented-method signature we hit.

Same class of gap as #1510, #1044 and #1003 (all on `ApexStringValue`), which were closed in the 2026-06-30 pre-v5 sweep.

### Workaround

Replace `enumValue.toString()` with `enumValue.name()`, which sfge does model. Semantically equivalent for standard enums.

### Urgency

Moderate

Beginne bei ApexEnumValue.java ungefähr in Zeile 123 und verfolge die dort gezeigte Verarbeitung bis durch PathScopeVisitor.java. Führe den bereitgestellten sf code-analyzer-Befehl gegen die EnumToString-Reproduktion aus. Erledigt bedeutet, dass enum toString() den Einstiegspunkt nicht mehr abbricht, je nach Fall einen bestimmten oder unbestimmten Wert zurückgibt und die Analyse ohne Verlust der Abdeckung abgeschlossen wird.

Vom Indexierungsmodell aus dem Issue-Text verfasst.