Preserve casts when converting lombok.val to final var

[sullis]

What's changed?

LombokValToFinalVar built the final var declaration with a JavaTemplate, which re-prints the initializer expression. Re-printing can lose type information: a cast to a type variable such as (T) o came out mangled, because the template parse has no knowledge of the enclosing class's type parameters.

This replaces the template with a direct LST transformation:

• Build the var J.Identifier (as the existing no-initializer branch already did) and swap it in for the val type expression, so both code paths now share that construction.
• Prepend a final modifier only when one isn't already present, moving the original type expression's prefix onto the modifier so formatting is preserved.

The initializer is carried over untouched, so casts — including generic ones — survive the conversion. Behavior for declarations without an initializer is unchanged (still a plain var, per openrewrite/rewrite#5637).

Also included is a small unrelated test fix: UpgradeToJava25Test.upgradeToJava25 pinned maven-compiler-plugin to 3.15.x in an assertion pattern, which breaks as soon as a newer minor is released. The pattern now accepts any 3.15+ version.

Anything in particular you'd like reviewers to focus on?

The prefix/modifier juggling is the part worth a close look — the existing tests cover annotated, already-final, multi-variable, and comment-carrying declarations, and two new tests cover the casts: preserveCast ((String) "foo") and preserveGenericCast ((T) o).

I can't run the build locally — dependency resolution needs credentials for artifacts.codegenomeproject.org — so I'm relying on CI for verification.

Have you considered any alternatives or workarounds?

Keeping JavaTemplate and making it type-aware. Sidestepping the re-print entirely is simpler, and it also removes the divergence between the initializer and no-initializer code paths.

[sullis]

• Ready for review @greg-at-moderne

[sullis]

• CI build is green

[greg-at-moderne]

Thanks for the PR. Looks well designed and I appreciate the tests.