[Bug] PathUtils.equalsIgnoreSchemeIfOneIsS3 path comparison is inconsistent between same-scheme and cross-scheme branches

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/doris/issues) and found no similar issues.

### Version

master (`fe-foundation`, `org.apache.doris.foundation.util.PathUtils`).

### What's Wrong?

`PathUtils.equalsIgnoreSchemeIfOneIsS3(p1, p2)` compares two storage-location URIs treating the `s3` scheme as interchangeable with other object-store schemes. Its two branches used **inconsistent** rules:

- **Same scheme** → `p1.equalsIgnoreCase(p2)`: full-string, **case-insensitive**, trailing slash **significant**.
- **Cross-scheme (one is `s3`)** → compares `normalize(authority)`/`normalize(path)` with `Objects.equals`: **case-sensitive**, trailing slash **stripped**.

Consequences:

1. The result for one URI depends on the *other* URI's scheme. For example `s3://bucket/path/` vs `s3://bucket/path` are **unequal** (same-scheme branch), but `s3://bucket/path/` vs `cos://bucket/path` are **equal** (cross-scheme branch).
2. The same-scheme branch ignores case for the whole string, so it can wrongly equate case-sensitive S3 object keys (`s3://b/A` == `s3://b/a`).

The only caller is `HMSTransaction.prepareInsertExistingTable` (`fe-core`), which uses this to decide whether a Hive commit needs a rename — so inconsistent equality can lead to an incorrect rename decision.

### What You Expected?

A single, consistent rule regardless of whether the two schemes match: compare authority + path (scheme ignored when equal or when one side is `s3`), with trailing slashes insignificant and the comparison case-sensitive (object-storage keys are case-sensitive).

### How to Reproduce?

```java
// same pair, different "other" scheme -> different answer (inconsistent):
PathUtils.equalsIgnoreSchemeIfOneIsS3("s3://bucket/path/", "s3://bucket/path"); // false
PathUtils.equalsIgnoreSchemeIfOneIsS3("s3://bucket/path/", "cos://bucket/path"); // true

// same-scheme comparison wrongly ignores case:
PathUtils.equalsIgnoreSchemeIfOneIsS3("s3://bucket/A", "s3://bucket/a"); // true (should be false)
```

### Anything Else?

Fix proposed in the linked PR. It also hardens several edge cases surfaced during review (opaque URIs, percent-encoded slashes, triple-slash / network-path forms) by falling back to exact string comparison for inputs that are malformed for object storage.

### Are you willing to submit PR?

- [x] Yes I am willing to submit a PR!

Start with PathUtils.equalsIgnoreSchemeIfOneIsS3 in org.apache.doris.foundation.util.PathUtils, then inspect its only caller, HMSTransaction.prepareInsertExistingTable. Exercise the reproduction cases from the issue and review the handling of opaque, percent-encoded, triple-slash, and network-path forms. Done means comparison is consistent, case-sensitive, and ignores trailing slashes as specified, with malformed object-storage inputs using exact string comparison.

Written by the indexing model from the issue text.