Scala edges: move import/package extraction onto tree-sitter-scala

[nikolay-e]

The Scala import/package reader in edges/semantic/jvm.rs is regex, and it is
now on its fifth patch: the import-regex fix (#179), the import a}.{B panic
(1.14.0), and three more in 1.15.0 — Scala 3 as renames, multi-line brace
imports, nested package blocks (#215). The multi-line fix counts braces with a
hard bound (joined < 32) so an unbalanced file cannot swallow the rest of
itself: an honest bound, but a bound is not a parse.

tree-sitter-scala is already a dependency (the fragmenter uses it) and answers
all three structurally through import_declaration and package_clause.

What makes this bigger than a swap, and why it was not done in the same pass as
the #209 / #213 / #207 cleanup: the edge layer reads fragment CONTENT with regex
for every one of the 30+ languages — no parse tree reaches it. Parsing inside an
edge builder would be the first of its kind, with a per-fragment parse cost and
its own corpus calibration. It is Q-class: edge sets move, so the baseline moves.

Shape when picked up:

• parse Scala fragments once, reuse the tree for imports, package and extends;
• keep the regex path as the fallback for content the parser rejects;
• gate on the full YAML corpus, and record the baseline delta either way.

Standing rule this issue exists to enforce: the SECOND patch on a hand-written
parser for a language that already has a grammar is the signal to move to the
grammar.