Skip reporting coverage on main source files that aren't uniquely named

[romain-cureau]

What

DelphiCodeCoverageParser.indexInputFiles() builds its file-name index with
ImmutableSortedMap, whose build() throws on duplicate keys. The index is keyed by the
bare file name, so any two source files sharing a name make it throw:

java.lang.IllegalArgumentException: Multiple entries with same key:
  AlimProcess.pas=Outils/ICHCL/Alim/AlimProcess.pas
  and AlimProcess.pas=Integration/...

The exception is caught in parseReportFile, so the analysis completes — but the entire
coverage report is discarded, leaving the project at 0 % with only an ERROR line in the
scanner log to explain it.

Why it matters

Sharing a file name across units is ordinary in Delphi codebases. On the project where this
surfaced, 274 of 2012 files in scope share 92 names: MainForm.pas (×20),
SvcDefinitionsImpl.pas (×14, one per service), Main.pas (×10), CommonGateway_TLB.pas
(×10). These are conventions, not defects — excluding them would mean excluding the core of
the codebase.

The failure is all-or-nothing: that project's report covers 67 files, of which only 3
have an ambiguous name, yet all 67 were dropped.

What this changes

Ambiguous names are removed from the index and reported once, instead of aborting the whole
report. Coverage is still recorded for every file whose name is unique — 64 of 67 in the
case above, rather than none.

The ambiguity itself isn't resolvable here: Delphi Code Coverage identifies files by bare
name, with no path to disambiguate against. Skipping those entries and saying so seemed more
useful than losing everything.

Notes

• Behaviour is unchanged when no file name is shared.
• ImmutableSortedMap is no longer used in this class, so the import is removed.
• Adds testAmbiguousFileNamesDoNotDiscardTheWholeReport, which registers a second
  MainWindow.pas and asserts that Globals.pas coverage is still recorded while the
  ambiguous name is skipped. The full DelphiCoverageToolParserTest suite passes (10 tests).
• Verified end to end against a real report (67 source files, 43 949 lines, 3 451 covered) on
  SonarQube 26.1 with the plugin built from this branch: coverage went from unreported to
  7.5 %, with Coverage data skipped for 92 ambiguous file name(s) in the log.