perf(ext/node): improve `Buffer` from string performance (#24567)

Fixes https://github.com/denoland/deno/issues/24323

- Use a Buffer pool for `fromString`
- Implement fast call base64 writes
- Direct from string `create` method for each encoding op

```
$ deno bench -A bench.mjs # 1.45.1+fee4d3a
cpu: Apple M1 Pro
runtime: deno 1.45.1+fee4d3a (aarch64-apple-darwin)

benchmark                time (avg)             (min … max)       p75       p99      p999
----------------------------------------------------------- -----------------------------
Buffer.from base64      550 ns/iter     (490 ns … 1'265 ns)    572 ns    606 ns  1'265 ns
Buffer#write base64     285 ns/iter       (259 ns … 371 ns)    307 ns    347 ns    360 ns

$ ~/gh/deno/target/release/deno bench -A bench.mjs # this PR
cpu: Apple M1 Pro
runtime: deno dev (aarch64-apple-darwin)

benchmark                time (avg)             (min … max)       p75       p99      p999
----------------------------------------------------------- -----------------------------
Buffer.from base64      151 ns/iter       (145 ns … 770 ns)    148 ns    184 ns    648 ns
Buffer#write base64   62.58 ns/iter     (60.79 ns … 157 ns)  61.65 ns  75.79 ns    141 ns

$ node bench.mjs # v22.4.0
cpu: Apple M1 Pro
runtime: node v22.4.0 (arm64-darwin)

benchmark                time (avg)             (min … max)       p75       p99      p999
----------------------------------------------------------- -----------------------------
Buffer.from base64      163 ns/iter     (96.92 ns … 375 ns)  99.45 ns    127 ns    220 ns
Buffer#write base64   75.48 ns/iter     (74.97 ns … 134 ns)  75.17 ns  81.83 ns  96.84 ns
```

1 files changed, 35 insertions, 4 deletions

diff --git a/ext/web/lib.rs b/ext/web/lib.rs
index 89f1197e7..c8badbf8a 100644
--- a/ext/web/lib.rs
+++ b/ext/web/lib.rs
@@ -16,7 +16,6 @@ use deno_core::ByteString;
 use deno_core::OpState;
 use deno_core::Resource;
 use deno_core::ResourceId;
-use deno_core::ToJsBuffer;
 use deno_core::U16String;
 
 use encoding_rs::CoderResult;
@@ -62,6 +61,7 @@ deno_core::extension!(deno_web,
   parameters = [P: TimersPermission],
   ops = [
     op_base64_decode,
+    op_base64_write,
     op_base64_encode,
     op_base64_atob,
     op_base64_btoa,
@@ -130,12 +130,43 @@ deno_core::extension!(deno_web,
 );
 
 #[op2]
-#[serde]
-fn op_base64_decode(#[string] input: String) -> Result<ToJsBuffer, AnyError> {
+#[buffer]
+fn op_base64_decode(#[string] input: String) -> Result<Vec<u8>, AnyError> {
   let mut s = input.into_bytes();
   let decoded_len = forgiving_base64_decode_inplace(&mut s)?;
   s.truncate(decoded_len);
-  Ok(s.into())
+  Ok(s)
+}
+
+#[op2(fast)]
+#[smi]
+fn op_base64_write(
+  #[string] input: String,
+  #[buffer] buffer: &mut [u8],
+  #[smi] start: u32,
+  #[smi] max_len: u32,
+) -> Result<u32, AnyError> {
+  let tsb_len = buffer.len() as u32;
+
+  if start > tsb_len {
+    return Err(type_error("Offset is out of bounds"));
+  }
+
+  let max_len = std::cmp::min(max_len, tsb_len - start) as usize;
+  let start = start as usize;
+
+  if max_len == 0 {
+    return Ok(0);
+  }
+
+  let mut s = input.into_bytes();
+  let decoded_len = forgiving_base64_decode_inplace(&mut s)?;
+
+  let max_len = std::cmp::min(max_len, decoded_len);
+
+  buffer[start..start + max_len].copy_from_slice(&s[..max_len]);
+
+  Ok(max_len as u32)
 }
 
 #[op2]