Speed up Client.map by computing token only once for func and kwargs

[fjetter]

tokenization is unfortunately expensive at times. Especially if we're iterating over a large collection this can be expensive.

Note: The tokenize(tok, args) is also expensive but mostly because of the ctxmanager foo we're doing in tokenize so calling it often is expensive. We should think about a fast path for this

[jrbourbeau]

LGTM thanks @fjetter

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    25 files  ±0      25 suites  ±0   10h 14m 39s ⏱️ + 5m 12s
 4 122 tests ±0   4 007 ✅ +1    111 💤 ±0  4 ❌  - 1 
47 615 runs  ±0  45 503 ✅ +2  2 108 💤 ±0  4 ❌  - 2 

For more details on these failures, see this check.

Results for commit a86d739. ± Comparison against base commit 2e61816.