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

[littledivy]

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