Unblock op/write.t by registering format declarations

[fglock]

Parent: #1116

perl5_t/t/op/write.t currently aborts before its first assertion with Undefined format "main::OUT", blocking all 636 tests in the file.

Plan:

1. Preserve format declarations during JVM block emission so they register before write executes.
2. Add equivalent registration support for the interpreter backend.
3. Add focused project-owned regression coverage without modifying the Perl core test.
4. Validate against system Perl, both PerlOnJava backends, and the full make gate.

Acceptance: op/write.t no longer terminates at startup and the focused regression passes on JVM and interpreter.

[fglock]

Handoff: next target in op/write.t

The declaration-registration milestone is complete. op/write.t now reaches TAP 577/636, then terminates in the active-format case around lines 1904–1919.

Target: per-filehandle current-format state

Perl permits a filehandle's active format to differ from the handle's glob name:

select +(select(UNDEF), $~ = 'UNDEFFORMAT')[0];
write UNDEF;

IOOperator.write currently resolves a glob argument as its own format (main::UNDEF) and has no implementation of selected-handle $~ association. It should resolve the active format for that handle and retain it while write is executing, so undef *UNDEFFORMAT inside the format cannot invalidate the active invocation.

Suggested plan

1. Represent a handle's current format/top-format state, including $~ and $^ updates under select and dynamic local scope.
2. Make write FILEHANDLE resolve that handle's active format rather than assuming the glob name.
3. Keep the selected format alive for the duration of execution when its glob or the handle is freed inside the format.
4. Add focused project-owned coverage for the UNDEF/UNDEFFORMAT scenario; validate it with system Perl, JVM, and interpreter.

This is a contained next cluster and should prevent the current early termination, exposing the final 59 TAP assertions. The larger follow-up cluster is format argument evaluation (RuntimeFormat.evaluateExpression), including lexical variables, tied/overloaded values, ^ fields, and ~~ continuation semantics.