feat: add discovery_cache_timeout to ClientBuilder and rediscover() t…

[SIDHARTH20K4]

The SDK makes fresh network requests on every startup to discover homeserver versions, well-known info, and other discovery data, even though this data rarely changes. This adds unnecessary latency and load on the homeserver.

This PR adds:

• ClientBuilder::discovery_cache_timeout(Duration) to configure how long discovery data is considered fresh (default: 24h)
• Client::rediscover() to force a refresh of all cached discovery data

Closes #1469

• I've documented the public API changes in the appropriate changelog files (see Writing changelog entries).
• This PR was made with the help of AI.

Signed-off-by: Sidharth sidharth.120504@gmail.com

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

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_{Comparing SIDHARTH20K4:feat/discovery-cache-timeout (40d0c09) with main (8980b4b)}

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
510	1	509	0

View the top 1 failed test(s) by shortest run time

matrix-sdk::client::tests::test_rediscover

Stack Traces | 1.58s run time

thread 'client::tests::test_rediscover' (14485) panicked at .../src/client/mod.rs:3989:35:
called `Result::unwrap()` on an `Err` value: OAuth(Discovery(Http(Api(Server(MatrixError(Error { status_code: 404, body: NotJson { bytes: b"", deserialization_error: Error("EOF while parsing a value", line: 1, column: 0) } }))))))
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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