UHV: Runtime or config knobs for known behavioral differences

Runtime or config flags for the known behavioral differences in UHV:

Path normalization:

- [x] Preserve the case of hexadecimal digits within %-encoded triplets (UHV makes them uppercase)
- [x] Allow malformed %-encoded triplets (UHV rejects requests with malformed %-encoded sequences)
- [x] Translate `\` to `/` (UHV rejects with 400 requests with `\` in the URL path)
- [ ] Fix nested %-encoded sequences by changing leading % to %25 (UHV rejects requests with malformed %-encoded sequences)
- [x] %-encode and allow all characters with codepoints >= 0x80 for H/2
- [x] Allow unencoded space or TAB in path for H/2 and H/3
- [x] Allow " < > [ ] ^ ` { } \ | # in URL path
- [x] reject requests with %00 sequence when path_normalization is enabled.

Header validation:

- [ ] Allow any case `:scheme` for H/2
- [ ] Restrict the `:method` header to specific values for H/1
- [ ] The `:authority` header validation compatible with nghttp2
- [ ] Reject the `*` URI path unconditionally
- [ ] Allow leading and trailing whitespace in H/2 header values.