Merge bitcoin/bitcoin#30888: build: optimize .h generation in GenerateHeaderFrom{Raw,Json}.cmake

2a581144f28bad44de40122864f2f7b9fc5000de build: Minimize I/O operations in GenerateHeaderFromJson.cmake (Lőrinc)
aa003d1568b84372616e85b0295c1eb6b165c8a3 build: Minimize I/O operations in GenerateHeaderFromRaw.cmake (Lőrinc)

Pull request description:

  Follow up of the https://github.com/bitcoin/bitcoin/pull/30883 revert.

  Replaced multiple file writes with a single string template write.
  The raw content is first grouped into 8 byte chunks, followed by another regex replace which wraps them in `std::byte` or just the raw bytes, prefixed with `0x`.

  Tested the output with `diff -w` and they're the same - only whitespace differences because slightly different source formatting.

  ----

  Tested the `Raw` performance with:
  ```bash
  time cmake -DRAW_SOURCE_PATH=src/bench/data/block413567.raw -DHEADER_PATH=build/after/block413567.raw.h -DRAW_NAMESPACE=benchmark::data -P cmake/script/GenerateHeaderFromRaw.cmake
  ```

  Before:
  > 15.41s user 23.06s system 97% cpu 39.593 total

  After:
  > 0.77s user 0.06s system 97% cpu 0.849 total

  ----

  Tested the `Json` performance with:
  ```bash
  time cmake -DJSON_SOURCE_PATH=src/secp256k1/src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.json -DHEADER_PATH=build/after/ecdsa_secp256k1_sha256_bitcoin_test.json -P cmake/script/GenerateHeaderFromJson.cmake
  ````

  Before:
  > 3.57s user 6.01s system 94% cpu 10.136 total

  After:
  > 0.17s user 0.01s system 98% cpu 0.187 total

ACKs for top commit:
  maflcko:
    review ACK 2a581144f28bad44de40122864f2f7b9fc5000de 👒
  hebasto:
    ACK 2a581144f28bad44de40122864f2f7b9fc5000de.
  willcl-ark:
    tACK 2a581144f28bad44de40122864f2f7b9fc5000de

Tree-SHA512: 5e44f79d1c0dbb61d8b64f28d4c3c87a176981f72104b28800eef2037b0728076cbcf14ff07b05ff94d4e8800605586cfd5df00519db9027933c5943348c01d2

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