trace: make tracing available in non-debug builds

Add --trace-config to curl

Add curl_global_trace() to libcurl

Closes #11421

unit tests: use the unit test infrastructure better

Allow UNITTEST_STOP to return the error code, use the fail & abort
macros to indicate test failure and return success instead of fail

unit tests: use the unit test infrastructure better

Allow UNITTEST_STOP to return the error code, use the fail & abort
macros to indicate test failure and return success instead of fail if
the unit test can't test anything because of missing features at
compile-time. A couple of tests could never fail because they were
overriding the failure return code.

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http3: improvements across backends

- ngtcp2: using bufq for recv stream data
- internal stream_ctx instead of `struct HTTP` members
for quiche, ngtcp2 and msh3
- no more QUIC

http3: improvements across backends

- ngtcp2: using bufq for recv stream data
- internal stream_ctx instead of `struct HTTP` members
for quiche, ngtcp2 and msh3
- no more QUIC related members in `struct HTTP`
- experimental use of recvmmsg(), disabled by default
- testing on my old debian box shows no throughput improvements.
- leaving it in, but disabled, for future revisit
- vquic: common UDP receive code for ngtcp2 and quiche
- vquic: common UDP send code for ngtcp2 and quiche
- added pytest skips for known msh3 failures
- fix unit2601 to survive torture testing
- quiche: using latest `master` from quiche and enabling large download
tests, now that key change is supported
- fixing test_07_21 where retry handling of starting a stream
was faulty
- msh3: use bufq for recv buffering headers and data
- msh3: replace fprintf debug logging with LOG_CF where possible
- msh3: force QUIC expire timers on recv/send to have more than
1 request per second served

Closes #10772

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lib: add `bufq` and `dynhds`

Adding `bufq`:
- at init() time configured to hold up to `n` chunks of `m` bytes each.
- various methods for reading from and writing to it.
- `peek`

lib: add `bufq` and `dynhds`

Adding `bufq`:
- at init() time configured to hold up to `n` chunks of `m` bytes each.
- various methods for reading from and writing to it.
- `peek` support to get access to buffered data without copy
- `pass` support to allow buffer flushing on write if it becomes full
- use case: IO buffers for dynamic reads and writes that do not blow up
- distinct from `dynbuf` in that:
- it maintains a read position
- writes on a full bufq return CURLE_AGAIN instead of nuking itself
- Init options:
- SOFT_LIMIT: allow writes into a full bufq
- NO_SPARES: free empty chunks right away
- a `bufc_pool` that can keep a number of spare chunks to
be shared between different `bufq` instances

Adding `dynhds`:
- a straightforward list of name+value pairs as used for HTTP headers
- headers can be appended dynamically
- headers can be removed again
- headers can be replaced
- headers can be looked up
- http/1.1 formatting into a `dynbuf`
- configured at init() with limits on header counts and total string
sizes
- use case: pass a HTTP request or response around without being version
specific
- express a HTTP request without a curl easy handle (used in h2 proxy
tunnels)
- future extension possibilities:
- conversions of `dynhds` to nghttp2/nghttp3 name+value arrays

Closes #10720

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