Fix SCM path normalization edge cases in ModelInheritanceAssembler (#274)

[elharo]

Fixes #274

Problem

ModelInheritanceAssembler.appendPath/resolvePath (used for inherited SCM
connection/url values in supplemental models) had edge-case inaccuracies:

• trailing slashes were dropped, so http://host/repo/ normalized to
  http://host/repo
• excess .. segments were silently swallowed (an acknowledged FIXME, no
  warning)
• empty segments (//) were removed and . segments were kept, inconsistently

Fix

Rewrote resolvePath using the JDK java.nio.file.Path.normalize() (no plexus
dependency for the new code):

• trailing separators are now preserved
• redundant separators, . and resolvable .. segments are collapsed
• excess .. segments are detected instead of being silently dropped

Test

New unit test class ModelInheritanceAssemblerTest (5 tests):

• trailing slash is preserved (fails before the fix)
• . segments are collapsed (fails before the fix)
• a warning is emitted for excess .. segments (fails before the fix)
• child appending and resolvable .. normalization still work (regression)

All existing tests pass: mvn verify -Prun-its (15 unit + 9 failsafe ITs,
incl. ITSupplementalArtifact which exercises supplemental-model merging),
plus spotless/checkstyle/RAT.

[elharo]

It isn't worth introducing a publc setLog method for this. Just don't log if this is required to log.

[elharo]

Removed the public setLog method and the excess-'..' warning entirely; resolvePath now just normalizes (the normalizer keeps excess '..' segments instead of silently dropping them, without logging).