time: optimize time <-> date conversions

time: optimize time <-> date conversions

Optimize the time -> date and date -> time conversions using the
methods outlined in:

    Cassio Neri and Lorenz Schneider,
    “Euclidean affine functions and their
    application to calendar algorithms,”
    SP&E 2023. https://doi.org/10.1002/spe.3172

I took the opportunity to introduce some types to make the code
significantly clearer and optimize a few other parts I noticed along
the way. The result is noticeably faster across the board.

Probably this doesn't matter much in real programs, but all the other
languages are picking this up, and it is less code than what we had
before.

Proposal #63844 suggested adopting this algorithm and simultaneously
restricting the range of valid years supported by the package from its
current ±292277022399 (plenty for anyone) to a mere ±32767.
This CL does NOT make any such restriction. The range of valid years
is almost exactly what it was before. (It is the same size but shifted
10 months earlier, which no one will ever care about.)

This CL removes any real need to consider the proposal, since it
would be a breaking change for truly insignificant benefit.

Thanks to Normandes Junior and Cassio Neri for CL 548155
and for discussion on #63844, which prompted me to write this CL.
This CL is all new code and does not include code from CL 548155
except as noted in the isLeap function implementation.

For #63844.

goos: linux
goarch: amd64
pkg: time
cpu: AMD Ryzen 9 7950X 16-Core Processor
                        │ timeold.txt  │             timenew.txt              │
                        │    sec/op    │   sec/op     vs base                 │
Format-32                  156.5n ± 1%   148.1n ± 1%   -5.37% (n=125)
FormatRFC3339-32           118.5n ± 1%   112.1n ± 1%   -5.40% (n=125)
FormatRFC3339Nano-32       119.2n ± 1%   113.0n ± 1%   -5.20% (n=125)
FormatNow-32               96.88n ± 2%   97.22n ± 1%        ~ (p=0.173 n=125)
MarshalJSON-32             79.77n ± 1%   75.82n ± 1%   -4.95% (n=125)
MarshalText-32             79.25n ± 1%   76.18n ± 1%   -3.87% (p=0.000 n=125)
Parse-32                   79.80n ± 1%   78.28n ± 1%   -1.90% (p=0.000 n=125)
ParseRFC3339UTC-32         29.10n ± 1%   28.90n ± 0%        ~ (p=0.094 n=125)
ParseRFC3339UTCBytes-32    30.72n ± 1%   30.88n ± 1%        ~ (p=0.894 n=125)
ParseRFC3339TZ-32          92.29n ± 0%   90.27n ± 1%   -2.19% (p=0.000 n=125)
ParseRFC3339TZBytes-32     133.4n ± 1%   132.0n ± 1%        ~ (p=0.004 n=125)
ParseDuration-32           41.11n ± 3%   44.08n ± 2%        ~ (p=0.088 n=125)
Hour-32                    2.834n ± 0%   2.829n ± 1%        ~ (p=0.891 n=125)
Second-32                  2.811n ± 1%   2.828n ± 1%        ~ (p=0.208 n=125)
Date-32                    9.228n ± 1%   5.788n ± 0%  -37.28% (n=125)
Year-32                    6.404n ± 1%   4.673n ± 1%  -27.03% (n=125)
YearDay-32                 6.399n ± 1%   5.802n ± 0%   -9.33% (n=125)
Month-32                   9.108n ± 1%   4.700n ± 1%  -48.40% (n=125)
Day-32                     9.106n ± 1%   4.686n ± 1%  -48.54% (n=125)
ISOWeek-32                10.060n ± 0%   7.998n ± 1%  -20.50% (n=125)
GoString-32                84.59n ± 1%   83.82n ± 1%        ~ (p=0.027 n=125)
DateFunc-32                6.993n ± 0%   6.144n ± 1%  -12.14% (n=125)
UnmarshalText-32           94.78n ± 2%   89.49n ± 1%   -5.58% (n=125)
geomean                    29.60n        26.13n       -11.70%

goos: darwin
goarch: arm64
pkg: time
cpu: Apple M3 Pro
                        │ timeold-m3.txt │            timenew-m3.txt            │
                        │     sec/op     │   sec/op     vs base                 │
Format-12                    152.6n ± 0%   147.4n ± 0%   -3.41% (n=125)
FormatRFC3339-12            101.50n ± 0%   92.02n ± 0%   -9.34% (n=125)
FormatRFC3339Nano-12        101.30n ± 0%   92.68n ± 0%   -8.51% (n=125)
FormatNow-12                 93.50n ± 0%   94.65n ± 0%   +1.23% (p=0.000 n=125)
MarshalJSON-12               50.06n ± 0%   48.25n ± 0%   -3.62% (n=125)
MarshalText-12               49.70n ± 0%   47.51n ± 0%   -4.41% (n=125)
Parse-12                     97.91n ± 0%   95.90n ± 0%   -2.05% (n=125)
ParseRFC3339UTC-12           36.45n ± 0%   35.78n ± 1%   -1.84% (n=125)
ParseRFC3339UTCBytes-12      38.11n ± 0%   37.42n ± 0%   -1.81% (n=125)
ParseRFC3339TZ-12           100.80n ± 1%   97.58n ± 0%   -3.19% (n=125)
ParseRFC3339TZBytes-12       111.8n ± 1%   107.4n ± 0%   -3.94% (n=125)
ParseDuration-12             52.70n ± 0%   52.84n ± 0%        ~ (p=0.028 n=125)
Hour-12                      2.657n ± 0%   2.655n ± 0%        ~ (p=0.018 n=125)
Second-12                    2.656n ± 0%   2.654n ± 0%        ~ (p=0.084 n=125)
Date-12                      8.201n ± 0%   5.055n ± 0%  -38.36% (n=125)
Year-12                      5.694n ± 0%   4.086n ± 0%  -28.24% (n=125)
YearDay-12                   5.693n ± 0%   4.828n ± 0%  -15.19% (n=125)
Month-12                     8.206n ± 0%   4.231n ± 0%  -48.44% (n=125)
Day-12                       8.199n ± 0%   4.551n ± 0%  -44.49% (n=125)
ISOWeek-12                   9.032n ± 0%   7.298n ± 0%  -19.20% (n=125)
GoString-12                  62.78n ± 0%   60.61n ± 0%   -3.46% (n=125)
DateFunc-12                  7.318n ± 0%   6.431n ± 0%  -12.12% (n=125)
UnmarshalText-12             99.66n ± 0%   95.64n ± 0%   -4.03% (n=125)

Change-Id: I089a072a731914702f8087018d00960e129f86b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/586257
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>