java.io: full File API + byte/char streams over Chez ports

Expand java.io so libraries that touch the filesystem work unchanged.

File: the full method surface — length, lastModified, can{Read,Write,Execute},
isHidden, list, mkdir(s), delete, createNewFile, renameTo, getParentFile,
get{Absolute,Canonical}File, compareTo/equals/hashCode — plus the statics
separator / pathSeparator / createTempFile / listRoots. A File now keeps the
path as given (new File("rel").getPath() is "rel", .isAbsolute false); a
relative path resolves against JOLT_PWD only when the filesystem is touched,
matching the JVM. slurp/spit and the dir helpers go through the same
resolution, fixing a spit-vs-slurp inconsistency.

Streams (host/chez/io-streams.ss) — each a jhost wrapping a Chez port, so
buffering, EOF and binary<->char transcoding come from Chez:
- FileInputStream / FileOutputStream / ByteArrayInputStream /
  ByteArrayOutputStream / BufferedInputStream / BufferedOutputStream
- FileReader / FileWriter / InputStreamReader / OutputStreamWriter /
  BufferedReader / BufferedWriter
Buffered* return the wrapped stream (Chez ports are already buffered).

clojure.java.io: input-stream/output-stream now yield real byte streams (were
aliased to the char reader/writer); added copy (byte-exact for byte sources),
make-parents, delete-file. with-open also closes file-writer/port-writer/
print-writer (a pre-existing gap).

All runtime shims, no re-mint. 15 JVM-certified corpus rows; make test +
shakesmoke green.

docs/host-interop.md

@@ -70,12 +70,29 @@ aren't implemented; a few are accepted but no-ops (noted inline).
 
 ### I/O
 
-- **`java.io.File`** — `(File. path)` / `(File. parent child)`; `getPath`
-  `getName` `getAbsolutePath` `getCanonicalPath` `toURI` `toURL` `exists`
-  `isDirectory` `isFile` `listFiles` `getParent`.
-- **`java.io.StringReader` / `StringWriter` / `PushbackReader`** — the
-  `read`/`readLine`/`mark`/`reset`/`unread`/`write`/`append`/`toString` surface
-  the reader and `with-out-str` rely on.
+- **`java.io.File`** — `(File. path)` / `(File. parent child)`. A File keeps the
+  path as given (`(.getPath (File. "rel"))` is `"rel"`, `.isAbsolute` false); a
+  relative path resolves against `JOLT_PWD` only when the filesystem is touched.
+  Methods: `getPath` `getName` `getParent` `getParentFile` `getAbsolutePath`
+  `getAbsoluteFile` `getCanonicalPath` `getCanonicalFile` `toURI` `toURL`
+  `exists` `isDirectory` `isFile` `isAbsolute` `isHidden` `length` `lastModified`
+  `canRead` `canWrite` `canExecute` `list` `listFiles` `mkdir` `mkdirs` `delete`
+  `createNewFile` `renameTo` `compareTo` `equals` `hashCode`. Statics:
+  `File/separator` `File/separatorChar` `File/pathSeparator` `File/createTempFile`
+  `File/listRoots`.
+- **Byte streams** — `FileInputStream` / `FileOutputStream` (over a path/File,
+  `append` arg), `ByteArrayInputStream` / `ByteArrayOutputStream`
+  (`toByteArray`/`toString`/`size`/`reset`), `BufferedInputStream` /
+  `BufferedOutputStream`. `read`/`read(byte[])`, `write(int)`/`write(byte[])`,
+  `flush`, `close`. Each is a Chez binary port underneath.
+- **Char streams** — `FileReader` / `InputStreamReader` (read a byte stream as
+  UTF-8), `FileWriter` / `OutputStreamWriter`, `BufferedReader` (`readLine`,
+  `lines`) / `BufferedWriter` (`newLine`), `StringReader` / `StringWriter` /
+  `PushbackReader`.
+- **`clojure.java.io`** — `file` `as-file` `reader` `writer` `input-stream`
+  `output-stream` `copy` (byte-exact for byte sources) `make-parents`
+  `delete-file` `resource` `as-url`. `slurp`/`spit`/`line-seq`/`with-open` work
+  over all of the above.
 - **`java.lang.ClassLoader`** — `getSystemClassLoader`, `.getResource`,
   `.getResourceAsStream` (resolved against the source roots).